Summary: This looks at the Biblical doctrine of the Trinity from the testimonies of the church fathers and from the Old Testament.
Historically, the greatest attack on the doctrine of the Trinity has been targeted at the person of Jesus Christ. Heresy has primarily centered around the question of ‘who Jesus is’. Therefore, up to this point I have focused on the identity and deity of Jesus Christ. If someone does not believe that Jesus is fully God, they can’t understand the concept of the Trinity. If Jesus was not fully God, He is no different than Mohammed, Buddha and countless other religious icons claimed by the world religions. If Jesus was merely a man, the world would be correct in its claim that all religions point to the same God. However, since Jesus was God, He has the right to claim that no one comes to the Father except by Him. No longer is the cross just another symbol, but it is the doorway to salvation that God Himself created by His own sacrifice and His own blood. Because Jesus is God, all the other religions challenge our allegiance to the one true God. God did not pay our debt to sin through Buddha. God did not provide works or methods in which to redeem ourselves. God paid our debt by becoming our sin so that we can become His righteousness through Jesus Christ. As Jesus said, “Most assuredly, I say to you, he who does not enter the sheepfold by the door, but climbs up some other way, the same is a thief and a robber.” (John 10:1 (quickview) ).
So we can see that this is an essential doctrine. On the deity and eternal personhood of Christ, the Christian faith hangs. Other religions claim to be Christian, but unless they come through the door of the cross, they and their leaders are robbers and thieves. There is no other way. Only God has the right to pay for sins and only God can redeem our souls from the justice demanded by the law. I can’t redeem myself, nor can any religious icon. Only Jesus Christ was God and only He has the right to pardon our sins. Only He paid the debt so I could be pardoned.
The first point of contention in the question of the Trinity is, ‘who gets to define what the Trinity means’? Anti-Trinitarians argue that the Trinity means three persons, thus there are three gods. However, it only makes sense to allow those who hold a certain doctrine to be the ones who define what the doctrine teaches. In this sense, rather than presenting the definition in my words, I will let the early church speak. In 160 AD, Athenagoras wrote that the church believes:
“they hold the Father to be God, and the Son God, and the Holy Spirit, and declare their union and their distinction in order.”
The church believed that the Father, Son and Holy Spirit are God in one union and distinct from each other. Iranaeus spelled the Trinitarian belief with the following statement:
The Church, though dispersed throughout the whole world, even to the ends of the earth, has received from the apostles and their disciples this faith: ...one God, the Father Almighty, Maker of heaven, and earth, and the sea, and all things that are in them; and in one Christ Jesus, the Son of God, who became incarnate for our salvation; and in the Holy Spirit, who proclaimed through the prophets the dispensations of God, and the advents, and the birth from a virgin, and the passion, and the resurrection from the dead, and the ascension into heaven in the flesh of the beloved Christ Jesus, our Lord, and His manifestation from heaven in the glory of the Father ‘to gather all things in one,’ and to raise up anew all flesh of the whole human race, in order that to Christ Jesus, our Lord, and God, and Savior, and King, according to the will of the invisible Father, ‘every knee should bow, of things in heaven, and things in earth, and things under the earth, and that every tongue should confess; to him, and that He should execute just judgment towards all.