Why I believe in the Trinity?
Based on the verses below, the Bible is clear that there is One God. Yet, the Bible is also clear that the Father, the Son, and the Holy Spirit are each separately called God. The church has wrestled with this issue and has explained this mystery by describing God as the Eternal Triune God. In short, The Father, Son, and Holy Spirit are three different and distinct persons (not modes of the same person), but they are One in their nature, essence, and being.
The Baptist Faith and Message describes the trinity as follows:
The eternal triune God reveals Himself to us as Father, Son, and Holy Spirit, with distinct personal attributes, but without division of nature, essence, or being.
The Westminster Larger Catechism, the 1648 document agreed to by the churches in Scottland, Ireland, and Englend describes the trinity as shown below:
Q. 8. Are there more Gods than one?
A. There is but one only, the living and true God.
Q. 9. How many persons are there in the Godhead?
A. There be three persons in the Godhead, the Father, the Son, and the Holy Ghost; and these three are one true, eternal God, the same in substance, equal in power and glory; although distinguished by their personal properties.
Q. 10. What are the personal properties of the three persons in the Godhead?
A. It is proper to the Father to beget the Son, and to the Son to be begotten of the Father, and to the Holy Ghost to proceed from the Father and the Son from all eternity.
Q. 11. How doth it appear that the Son and the Holy Ghost are God equal with the Father?
A. The Scriptures manifest that the Son and the Holy Ghost are God equal with the Father, ascribing unto them such names, attributes, works, and worship, as are proper to God only.
And, the most complete statement about the trinity is contained in the The Athanasian Creed quoted at the bottom of this post.
Verses to Consider:
A. The Bible teaches there is only one God.
Mark 12:29 (NET)
29 Jesus answered, “The most important is: ‘Listen, Israel, the Lord our God, the Lord is one.
1 Timothy 1:17 (NET)
17 Now to the eternal king, immortal, invisible, the only God, be honor and glory forever and ever! Amen.
B. Yet the Bible teaches The Father is God, the Son is God, and the Holy Spirit is God.
The Father is God
1 Corinthians 8
6 yet for us there is one God, the Father, from whom are all things and for whom we live, and one Lord, Jesus Christ, through whom are all things and through whom we live.
Jesus is God and Creator and is from Everlasting
Micah 5:2 (KJV) But thou, Bethlehem Ephratah, [though] thou be little among the thousands of Judah, [yet] out of thee shall he come forth unto me [that is] to be ruler in Israel; whose goings forth [have been] from of old, from everlasting.
The Gospel of John
1 In the beginning was the Word, and the Word was with God, and the Word was fully God. 2 The Word was with God in the beginning. 3 All things were created by him, and apart from him not one thing was created that has been created.
14 Now the Word became flesh and took up residence among us. We saw his glory – the glory of the one and only, full of grace and truth, who came from the Father.
John 8:58 (NET) 58 Jesus said to them, “I tell you the solemn truth, before Abraham came into existence, I am!” – (I am is the name God used for Himself in Exodus 3:13-14).
Romans 9:5 (NET) 5 To them belong the patriarchs, and from them, by human descent, came the Christ, who is God over all, blessed forever! Amen.
Titus 2:13 (NET) 13 as we wait for the happy fulfillment of our hope in the glorious appearing of our great God and Savior, Jesus Christ.
Hebrews 1:8 (NET) 8 but of the Son he says, “Your throne, O God, is forever and ever, and a righteous scepter is the scepter of your kingdom.
Colossians 1 (NET)
1:13 He delivered us from the power of darkness and transferred us to the kingdom of the Son he loves, 1:14 in whom we have redemption, the forgiveness of sins. 1:15 He is the image of the invisible God, the firstborn over all creation, 1:16 for all things in heaven and on earth were created by him – all things, whether visible or invisible, whether thrones or dominions, whether principalities or powers – all things were created through him and for him.
The Holy Spirit is God
Genesis 1:2 Now the earth was without shape and empty, and darkness was over the surface of the watery deep, but the Spirit of God was moving over the surface of the water. 1:3 God said, “Let there be light.” And there was light!
Job 33:4 The Spirit of God has made me, and the breath of the Almighty gives me life.
Mathew 12:31 For this reason I tell you, people will be forgiven for every sin and blasphemy, but the blasphemy against the Spirit will not be forgiven.
Mathew 28:18 Then Jesus came up and said to them, “All authority in heaven and on earth has been given to me. 28:19 Therefore go and make disciples of all nations, baptizing them in the name of the Father and the Son and the Holy Spirit, 28:20 teaching them to obey everything I have commanded you. And remember, I am with you always, to the end of the age.”
Acts 5:3 (NET) 3 But Peter said, “Ananias, why has Satan filled your heart to lie to the Holy Spirit and keep back for yourself part of the proceeds from the sale of the land? 4 Before it was sold, did it not belong to you? And when it was sold, was the money not at your disposal? How have you thought up this deed in your heart? You have not lied to people but to God!”
1 Corinthians 2:11 For who among men knows the things of a man except the man’s spirit within him? So too, no one knows the things of God except the Spirit of God.
1 Corinthians 3:16 Do you not know that you are God’s temple and that God’s Spirit lives in you? 3:17 If someone destroys God’s temple, God will destroy him. For God’s temple is holy, which is what you are.
Hebrews 9:14 how much more will the blood of Christ, who through the eternal Spirit offered himself without blemish to God, purify our consciences from dead works to worship the living God.
1 Peter 1:20 Above all, you do well if you recognize this: No prophecy of scripture ever comes about by the prophet’s own imagination, 1:21 for no prophecy was ever borne of human impulse; rather, men carried along by the Holy Spirit spoke from God.
C. The three are eternally distinct persons, not merely modes of the same person.
See verses below showing the persons of the Godhead talking to each other and being all present at the same time, therefore, they are not modes of the same person but are three distinct persons which exist simultaneously.
All three together at once
Genesis 1:26 (NET)
Then God said, “Let us make humankind in our image, after our likeness, so they may rule over the fish of the sea and the birds of the air, over the cattle, and over all the earth, and over all the creatures that move on the earth.”
Mathew 3:16 After Jesus was baptized, just as he was coming up out of the water, the heavens opened and he saw the Spirit of God descending like a dove and coming on him. 3:17 And a voice from heaven said, “This is my one dear Son; in him I take great delight.”
The Father and Son together
Mathew 17:5 While he was still speaking, a bright cloud overshadowed them, and a voice from the cloud said, “This is my one dear Son, in whom I take great delight. Listen to him!”
The Father sends the Holy Spirit in the name of Jesus
John 14:26 But the Advocate, the Holy Spirit, whom the Father will send in my name, will teach you everything, and will cause you to remember everything I said to you.
Therefore, based on these scriptures, you can see how the church developed the conept of the Trinity to describe God in a way that takes all the above Bible verses into account.
A very good link for more Trinity verses.
The Athanasian Creed
Whoever wishes to be saved, needs above all to hold the Catholic (Catholic means the universal faith, not the Roman Catholic Church) faith; unless each one preserves this whole and inviolate, he will without a doubt perish in eternity.
But the Catholic faith is this, that we venerate one God in the Trinity, and the Trinity in oneness; neither confounding the persons, nor dividing the substance; for there is one person of the Father, another of the Son, and another of the Holy Spirit; but the divine nature of the Father and of the Son and of the Holy Spirit is one, their glory is equal, their majesty is coeternal.
Of such a nature as the Father is, so is the Son, so also is the Holy Spirit; the Father is uncreated, the Son is uncreated, and the Holy Spirit is uncreated; the Father is infinite, the Son is infinite, and the Holy Spirit is infinite; the Father is eternal, the Son is eternal, and the Holy Spirit is eternal; and nevertheless there are not three eternals but one eternal; just as there are not three uncreated beings, nor three infinite beings, but one uncreated, and one infinite; similarly the Father is almighty, the Son is almighty, and the Holy Spirit is almighty; and yet there are not three almightys but one almighty; thus the Father is God, the Son is God, and the Holy Spirit is God; and nevertheless there are not three gods, but there is one God; so the Father is Lord, the Son is Lord, and the Holy Spirit is Lord; and yet there are not three lords, but there is one Lord; because just as we are compelled by Christian truth to confess singly each one person as God, and also Lord, so we are forbidden by the Catholic religion to say there are three gods or three Lords.
The Father was not made, nor created, nor begotten by anyone. The Son is from the Father alone, not made nor created, but begotten. The Holy Spirit is from the Father and the Son, not made, nor created, nor begotten, but proceeding.
There is, therefore, one Father, not three Fathers; one Son, not three Sons; one Holy Spirit, not three Holy Spirits; and in this Trinity there is nothing first or later, nothing greater or less, but all three Persons are coeternal and coequal with one another, so that in every respect, as has already been said above, both unity in Trinity, and Trinity in unity must be venerated. Therefore, let him who wishes to be saved, think thus concerning the Trinity.
But it is necessary for eternal salvation that he faithfully believes also the incarnation of our Lord Jesus Christ.
Accordingly, it is the right faith, that we believe and confess, that our Lord Jesus Christ, the Son of God is God and man. He is God begotten of the substance of the Father before time, and He is man born of the substance of His mother in time: perfect God, perfect man, consisting of a rational soul and a human body, equal to the Father according to His Godhead, less than the Father according to humanity.
Although he is God and man, yet He is not two, but He is one Christ; one however, not by the conversion of the Divinity into a human body, but by the assumption of humanity in the Godhead; one absolutely not by confusion of substance, but by unity of person. For just as the rational soul and body are one man, so God and man are one Christ.
He suffered for our salvation, descended into hell, on the third day arose again from the dead, ascended into heaven, sits at the right hand of God the Father Almighty; thence He shall come to judge the living and the dead; at His coming all men have to arise again with their bodies and will render an account of their own deeds: and those who have done good, will go into life everlasting, but those who have done evil, into eternal fire.
This is the Catholic faith; unless every one believes this faithfully and firmly, he cannot be saved. Amen.