The Bible says repeatedly that there is only one God:
“ Hear, O Israel! The L ord is our God, the L ord is one!” (Deut. 6:4).
“ To you it was shown that you might know that the L ord, He is God; there is no other besides Him.… Know therefore today, and take it to your heart, that the L ord, He is God in heaven above and on the earth below; there is no other” (Deut. 4:35, 39).
"See now that I, I am He, And there is no god besides Me…" (Deuteronomy 32:39).
"so that all the peoples of the earth may know that the Lord is God; there is no one else" (1 Kings 8:60).
“‘You are My witnesses,’ declares the LORD, ‘And My servant whom I have chosen, So that you may know and believe Me And understand that I am He. Before Me there was no God formed, And there will be none after Me. I, even I, am the LORD, And there is no savior besides Me. It is I who have declared and saved and proclaimed, And there was no strange god among you; So you are My witnesses,’ declares the LORD, ‘And I am God. Even from eternity I am He’” (Isa. 43:10-13a).
“Thus says the LORD, the King of Israel and his Redeemer, the LORD of hosts: ‘I am the first and I am the last, And there is no God besides Me.… Is there any God besides Me, Or is there any other Rock? I know of none’” (Isaiah 44:6, 8b).
“I am the Lord, and there is no other; Besides Me there is no God. I will gird you, though you have not known Me; That men may know from the rising to the setting of the sun That there is no one besides Me. I am the Lord, and there is no other, The One forming light and creating darkness, Causing well-being and creating calamity; I am the Lord who does all these” (Isaiah 45:5-7).
“For thus says the Lord, who created the heavens (He is the God who formed the earth and made it, He established it and did not create it a waste place, but formed it to be inhabited), “I am the Lord, and there is none else. “I have not spoken in secret, In some dark land; I did not say to the offspring of Jacob, ‘Seek Me in a waste place’; I, the Lord, speak righteousness, Declaring things that are upright. “Gather yourselves and come; Draw near together, you fugitives of the nations; They have no knowledge, Who carry about their wooden idol And pray to a god who cannot save. “Declare and set forth your case; Indeed, let them consult together. Who has announced this from of old? Who has long since declared it? Is it not I, the Lord? And there is no other God besides Me, A righteous God and a Savior; There is none except Me. “Turn to Me and be saved, all the ends of the earth; For I am God, and there is no other” (Isaiah 45:18-22).
"Therefore concerning the eating of things sacrificed to idols, we know that there is no such thing as an idol in the world, and that there is no God but one" (1 Corinthians 8:4).
"Now a mediator is not for one party only; whereas God is only one" (Galatians 3:20).
“For there is one God, and one mediator also between God and men, the man Christ Jesus” (1 Tim. 2:5).
“…Our Lord Jesus Christ, … He who is the blessed and only Sovereign, the King of kings and Lord of lords, who alone possesses immortality and dwells in unapproachable light, whom no man has seen or can see. To Him be honor and eternal dominion! Amen” (1 Tim. 6:14-16).
“You believe that God is one. You do well; the demons also believe, and shudder” (James 2:19).
The Bible also indicates there are multiple divine Persons. In the Old Testament this is more intimated than explicit; in only one verse, Isaiah 48:16, is there an indication of the specific number of Persons. In the New Testament it becomes clear and explicit that there are three, Father, Son, and Holy Spirit.
“In the beginning God created the heavens and the earth. The earth was formless and void, and darkness was over the surface of the deep, and the Spirit of God was moving over the surface of the waters.…Then God said, “Let Us make man in Our image, according to Our likeness; …” (Genesis 1:1-2, 26).
“Come, let Us go down and there confuse their language…” (Genesis 11:7).
“I will surely tell of the decree of the Lord: He said to Me, ‘You are My Son, Today I have begotten You” (Psalm 2:7).
“The Lord says to my Lord: ‘Sit at My right hand until I make Your enemies a footstool for Your feet’” (Psalm 110:1).
“Who has ascended into heaven and descended? Who has gathered the wind in His fists? Who has wrapped the waters in His garment? Who has established all the ends of the earth? What is His name or His son’s name? Surely you know!” (Proverbs 30:4).
“Therefore the Lord Himself will give you a sign: Behold, a virgin will be with child and bear a son, and she will call His name Immanuel” (Is 7:14).
“For a child will be born to us, a son will be given to us; And the government will rest on His shoulders; And His name will be called Wonderful Counselor, Mighty God, Eternal Father, Prince of Peace” (Is 9:6).
“Come near to Me, listen to this: From the first I have not spoken in secret, From the time it took place, I was there. And now the Lord G od has sent Me, and His Spirit” (Is 48:16). [Here Yahweh (Jehovah) is speaking, yet says Yahweh sent Him, and His Spirit. Yahweh sending Yahweh is also found in Zechariah 2:8-11. Compare John 1:1.]
“After being baptized, Jesus came up immediately from the water; and behold, the heavens were opened, and he saw the Spirit of God descending as a dove and lighting on Him, and behold, a voice out of the heavens said, ‘This is My beloved Son, in whom I am well-pleased’” (Matthew 3:16-17).
“Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit” (Matthew 28:19).
“I will ask the Father, and He will give you another Helper, that He may be with you forever; that is the Spirit of truth, whom the world cannot receive, because it does not see Him or know Him, but you know Him because He abides with you and will be in you” (John 14:16-17).
“When the Helper comes, whom I will send to you from the Father, that is the Spirit of truth who proceeds from the Father, He will testify about Me” (John 15:26).
“and hope does not disappoint, because the love of God has been poured out within our hearts through the Holy Spirit who was given to us. For while we were still helpless, at the right time Christ died for the ungodly” (Romans 5:5-6).
“But if the Spirit of Him who raised Jesus from the dead dwells in you, He who raised Christ Jesus from the dead will also give life to your mortal bodies through His Spirit who dwells in you” (Romans 8:11).
“The Spirit Himself testifies with our spirit that we are children of God, and if children, heirs also, heirs of God and fellow heirs with Christ, if indeed we suffer with Him so that we may also be glorified with Him” (Romans 8:16-17).
“Now there are varieties of gifts, but the same Spirit. And there are varieties of ministries, and the same Lord. There are varieties of effects, but the same God who works all things in all persons” (1 Corinthians 12:4-6).
“The grace of the Lord Jesus Christ, and the love of God, and the fellowship of the Holy Spirit, be with you all.” (2 Corinthians 13:14).
“But when the fullness of the time came, God sent forth His Son, born of a woman, born under the Law, so that He might redeem those who were under the Law, that we might receive the adoption as sons. Because you are sons, God has sent forth the Spirit of His Son into our hearts, crying, ‘Abba! Father!’” (Galatians 4:4-6).
“for through Him we both have our access in one Spirit to the Father” (Ephesians 2:18).
“There is one body and one Spirit, just as also you were called in one hope of your calling; one Lord, one faith, one baptism, one God and Father of all who is over all and through all and in all” (Ephesians 4:4-6).
“And do not get drunk with wine, for that is dissipation, but be filled with the Spirit, speaking to one another in psalms and hymns and spiritual songs, singing and making melody with your heart to the Lord; always giving thanks for all things in the name of our Lord Jesus Christ to God, even the Father” (Ephesians 5:18-20).
“We give thanks to God always for all of you, making mention of you in our prayers; constantly bearing in mind your work of faith and labor of love and steadfastness of hope in our Lord Jesus Christ in the presence of our God and Father, knowing, brethren beloved by God, His choice of you; for our gospel did not come to you in word only, but also in power and in the Holy Spirit and with full conviction; just as you know what kind of men we proved to be among you for your sake” (1 Thessalonians 1:2-5).
“But we should always give thanks to God for you, brethren beloved by the Lord, because God has chosen you from the beginning for salvation through sanctification by the Spirit and faith in the truth” (2 Thessalonians 2:13).
“But when the kindness of God our Savior and His love for mankind appeared, He saved us, not on the basis of deeds which we have done in righteousness, but according to His mercy, by the washing of regeneration and renewing by the Holy Spirit, whom He poured out upon us richly through Jesus Christ our Savior” (Titus 3:4-6).
“according to the foreknowledge of God the Father, by the sanctifying work of the Spirit, to obey Jesus Christ and be sprinkled with His blood: May grace and peace be yours in the fullest measure” (1 Peter 1:2).
“For Christ also died for sins once for all, the just for the unjust, so that He might bring us to God, having been put to death in the flesh, but made alive in the spirit” (1 Peter 3:18).
“By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God” (1 John 4:2).
“But you, beloved, building yourselves up on your most holy faith, praying in the Holy Spirit, keep yourselves in the love of God, waiting anxiously for the mercy of our Lord Jesus Christ to eternal life. And have mercy on some, who are doubting; save others, snatching them out of the fire; and on some have mercy with fear, hating even the garment polluted by the flesh. Now to Him who is able to keep you from stumbling, and to make you stand in the presence of His glory blameless with great joy, to the only God our Savior, through Jesus Christ our Lord, be glory, majesty, dominion and authority, before all time and now and forever. Amen” (Jude 20-4:21).
Many more scriptures could be adduced to show that each of these three Persons possesses the attributes of Deity, that each have the authority of Deity, that each have the power of Deity, and that each have been involved in works that only God could do. For our purposes here, however, the fact that each of these three Persons is God is sufficiently evident from the following verses:
Father:“Do not work for the food which perishes, but for the food which endures to eternal life, which the Son of Man will give to you, for on Him the Father, God, has set His seal” (John 6:27).
"Paul, an apostle (not sent from men nor through the agency of man, but through Jesus Christ and God the Father, who raised Him from the dead)" (Galatians 1:1).
Son:
"In the beginning was the Word, and the Word was with God, and the Word was God" (John 1:1).
“I and the Father are one” (John 10:30).
"looking for the blessed hope and the appearing of the glory of our great God and Savior, Christ Jesus" (Titus 2:13).
"But of the Son He says, “Your throne, O God, is forever and ever, And the righteous scepter is the scepter of His kingdom" (Hebrews 1:8).
Holy Spirit:
"But Peter said, “Ananias, why has Satan filled your heart to lie to the Holy Spirit and to keep back some of the price of the land? “While it remained unsold, did it not remain your own? And after it was sold, was it not under your control? Why is it that you have conceived this deed in your heart? You have not lied to men but to God” (Acts 5:3-4).
"Now the Lord is the Spirit, and where the Spirit of the Lord is, there is liberty" (2 Corinthians 3:17).
“In Christian usage the term Trinity expresses the belief that there is only “one God” (De 6:4; 1 Ti 2:5) who exists as three distinct divine persons, Father, Son, and Holy Spirit (Mt 28:19), who are cosubstantial, coeternal, and coequal. While each divine person has particular roles and functions (e.g., Eph 1:3–14), all three work together in perfect accord (Jn 5:17, 19; 10:28–30). The doctrine of the Trinity is to be distinguished (1) from tritheism, which teaches the existence of three gods rather than only one God (cf. De 6:4), and (2) from modalism, which denies the coexistence of the three divine persons by teaching that God exists and manifests Himself as only one divine person at once (cf. Mt 3:16–17).”(1)
The doctrine of the Trinity is not a doctrine that is appealing to the natural man, because it really is beyond our ability to comprehend. The natural man wants a God with no mystery, because that is a God he can control. But God simply defies any exhaustive comprehension by finite human beings. In the nature of His being God cannot be cornered by human reason, a fact that is galling to the unregenerate mind. For that very reason, no one would ever naturally invent the doctrine of the Trinity. No one would go there without being driven there by the scriptures.
The importance of the doctrine of the Trinity, as well as the natural man’s antipathy toward it, is underscored by the fact that virtually every counterfeit-Christianity group attacks it. Like the Cross, it is like a lightning rod for the ire and contempt of all the pseudo-Christian cults. They love, of course, to point out that the word Trinity itself is not found in scripture, as if that were news, and as if that disproved the doctrine signified by the word.
Jews and Muslims also attack the doctrine. They see the many affirmations of scripture that there is absolutely only one God, and then reason from there that if there is only one God, then there can be only one Person that is God. Mormons, on the other hand, see the clear New Testament teaching that three Persons—Father, Son, and Holy Spirit—are God, and then reason from there that if there are three Persons who are God, then there must be three Gods.
Christians know the word Trinity itself is not in the Bible. But they also know that all the constituent parts of the doctrine signified by that word are in the Bible. They say, “We are going to believe all that the Bible says about God, about the Father, the Son, and the Holy Spirit, and we refuse to blunt the edges on any of it. The Bible says there is only one God, and, there are three Persons who are God. Therefore, the one God is three Persons, and the three Persons are one God. We don’t care if we cannot understand how one Being can have three centers of consciousness; but when we add it up all together, that is how we find God describes Himself. And He should know. So we believe it!”
Those who believe the doctrine do not believe it because they understand it, but because they cannot escape it and still be true to all that the Bible tells us about God, about the Father, about the Son, and about the Holy Spirit. They would rather live with a mysterious God than defy His revelation of Himself.
Many analogies have been presented to try to make the triune nature of God more understandable: e.g., the egg—yolk, white, and shell; water—steam, liquid, and ice; light—wave, particle, and heat; space—height, length, and width; time—past, present, and future; human existence—body, soul, and spirit. The list could go on and on. But the fact is that ultimately every one of these analogies breaks down, fails, is insufficient, or worse, actually leads to some errors about God. They might be regarded as God’s fingerprints all over the creation, but they can never suffice to truly explain the nature of God’s existence as one Being with three centers of consciousness.
The fact remains that we know of no other such being, and simply have no real frame of reference with which to compare Him. This should not really be troubling, much less surprising, since God repeatedly asserts His own uniqueness. “Who is like Me,” He demands. “To whom (or what) will you liken Me?” Such questions appear frequently in the Old Testament. And in their context, the point of the questions is always that there is no one. Any other answer and you are arguing with God.
Are we saying then that man cannot know God? Does not the Bible, and even Jesus Himself say, “This is eternal life, that they may know You, the only true God, and Jesus Christ whom You have sent” (John 17:3)? One might say, “You’re telling me I cannot know God. That’s the same as telling me I cannot have eternal life!”
All we are saying here is that we cannot know God exhaustively. “Knowing God,” as Jesus spoke of it, is a matter of being in personal relationship with God. We do not need to have an exhaustive comprehension of God’s nature and being to “know Him” well enough to have a personal relationship with Him. It is not, primarily, by His nature and being that we have a relationship with Him anyway, but by His character. But even His character cannot be exhaustively comprehended. What we are given to know, however, of both His nature and His character, is sufficient to have a relationship with Him, while insufficient to remove all mystery from Him. That mystery must itself become a part of the relationship. If there were no mystery whatever, then the finite would have swallowed the infinite. The very idea is nonsense.
Think about it. Do you know any other person in your life exhaustively? Ask a man on the day of his wedding, “Do you really know your bride?” “Well of course I do,” he might reply. “What a silly question! Why else would I marry her?” Find the same man ten years later (or even one year or six months later) and ask him again if he really knew his wife when he married her. Well, yes, he knew her, but did he know her then the way he knows her now? Not hardly. It’s a matter of both the accuracy and the depth of perception and knowledge. (And the same phenomena will be observed by asking the wife, by the way.) The fact is, however long they live together after that, and however much better they come to know each other, in the end there will always still be a certain mystery, depths and inner recesses of the other’s soul, that they never quite fathomed. (And frankly, it would probably be rather boring if that were not so!)
But did they know each other? Did they have a real, personal relationship with each other? Yes, of course they did. Again, one does not need exhaustive knowledge of another to be in such relationship. And it should be obvious that if we can never have an exhaustive comprehension of even a finite being such as our spouse, it is absurd to think that the finite human being could or should have exhaustive comprehension of the infinite being of God. And it would be sheer hubris to refuse to believe in or relate to God so far as He has revealed Himself, simply because He cannot be exhaustively comprehended.
The fact is, no one will ever stand before God and be able to say, “I couldn’t believe in You, or in Your triune nature, because I couldn’t understand it.” God will simply point to the millions of believers who did and do believe it, and say, “None of these understood it any more than you. Yet they believed it, because that is how I revealed Myself to be, in My Word." It will be right, then—no one will object, and all the heavenly hosts, men and angels together, will say, Amen!—when that God whom they rejected in favor of worshiping a finite god of their own creation, finally rejects them.(1) The NASB Topical Index. electronic ed. La Habra, CA: The Lockman Foundation, 1998.