Belief in the Trinity is a central tenet of the Catholic Church and of most (if not all) of the Protestant denominations that trace their history back to her. The Catholics did not fully define the Godhead as composed of the Father, Son and Holy Spirit, or Trinity, until the end of the fourth century A.D. (more than 350 years after the birth of the New Testament church!).
The Catholic Church's official explanation of the Trinity is as follows.
"The Trinity is the term employed to signify the central doctrine of the Christian religion - the truth that in the unity of the Godhead there are Three Persons, the Father, the Son, and the Holy Spirit, these Three Persons being truly distinct one from another." (1913 Catholic Encyclopedia article on Blessed Trinity).
How much of a Christian litmus test is belief in the Trinity? Many people and denominations do not recognize a person as a true converted Christian, in spite of anything else in their life, if they do not believe this single doctrine! In fact, many "Christian" sites on the Internet will not allow ads on their pages from ANY advertiser that does not profess belief in the Trinity!
Amazingly, the Catholics admit in their own encyclopedia that belief in a triune Godhead did NOT come from in-depth Bible study or research. They state, "In Scripture there is as yet no single term by which the Three Divine Persons are denoted together . . ." (ibid.)!
The most popular and well-worn Bible verses used to 'prove' the Trinity is found in 1John 5, especially in the King James Version Bible. It states, "This is he that came by water and blood, [even] Jesus Christ; not by water only, but by water and blood . . . For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost . . . " (1John 5:6, 8, KJV).
Theologians, however, recognize that words, used to justify adopting the Trinity, were inserted into 1John 5 probably as late as the 8th century A.D. The JFB commentary states that the only Greek manuscripts which support the words "in heaven, the father, etc." is one from Dublin, and that it is apparent the words in question were added later to the margin.
The most accurate modern translation of these verses, which show they do not have anything to do with the Trinity, is "This is He Who came by water and blood - Jesus the Christ; not by water only, but by water and blood . . . For there are three that bear witness on the earth: the Spirit, and the water, and the blood" (1John 5:6, 8, HBFV).
Is Jesus the second person of a Trinity? He is the Spokesman for God Almighty and the Creator of all things as outlined in the Book of Genesis. He is also the Lord of the Old Testament who became Christ in the flesh in the Gospels. The apostle Paul makes it abundantly clear that Jesus was not only the Deity of the Old Testament but was also the Being that led the Israelites out of bondage (1Corinthians 10:1 - 4).
The Bible makes a distinction between Jesus Christ and God the Father. Jesus came to reveal the Father to the world as no one had seen him previously (John 1:18). Note that he came only to reveal the Father and not the Holy Spirit. If the Spirit was part of some kind of Trinity of the Godhead, then Jesus made a grave error by not revealing the depth of information he did about it (him?) as he did for the Eternal.
You can search the Bible from cover to cover, however, and you will not find ANYWHERE that states the Holy Spirit is God (which would be the case if the Trinity were true) just like the Father and Jesus. The Bible simply does not teach that the Holy Spirit is a third member of some triune Godhead.
The personality of Jesus is thoroughly provable from the Bible, but there is no such proof for the individuality and personality Holy Spirit. This information would clearly be in the inspired text IF the Godhead were a Trinity. Instead, in the Old Testament, God's Spirit is pictured as His power. It is the power by which the One who became Jesus Christ created the entire universe.
The Holy Spirit, rather than being a person of some Trinity, is the power of God through which Jesus came to the earth through Mary's womb (Matthew 1:18). This fact was confirmed by an angel who visited Joseph (verse 20). It is this same spirit, according to Paul the apostle, that he puts in the mind of those who are converted. It makes them one of God's children and gives them an opportunity to inherit all things through Christ (Romans 8:16, Hebrews 1:2, Galatians 4:7).
The Godhead is currently composed of only two Beings. They are God the Father and Jesus Christ. Scripture, however, reveals that it is actually a family where other beings can be added to it and not a closed Trinity! The original language word used in the Old Testament for God (the Godhead) is Elohim. It is a uniplural noun like our words "group" or "church" or "family." This word shows that the Godhead is indeed open to more members.
The Trinity doctrine hides God's purpose and plan for man. Such a teaching leads people astray from his purpose of adding far more members to his family. If we look at Genesis' account of creation we find sets of animals made after 'their kind.' In Genesis 1:26 we find man made after the Godkind, after our Creator's image and likeness. John the apostle fully understood why man was made in the first place.
What glorious love the Father has given to us, that we should be called the children of God! . . . and it has not yet been revealed what we shall be . . . we shall be like Him. (1John 3:1 - 2, HBFV)
The teaching that God is a Trinity is one of the chief false doctrines of the Roman Catholic Church. It is also one of the primary false teachings Protestants took with them when they left the Catholics during the Reformation. The Biblical truth is that the Holy Spirit is the power through which God begets us as his dear children. It is decidedly not a person or part of some Triune-based Godhead. Instead, it is the power by our Father and Jesus Christ accomplish their will.