What’s wrong? I didn’t claim that doctrine establishes truth. What are you talking about?
You said that “since the doctrine of the Trinity, as understood today, was not formulated until the 4th and 5th century, early Christians were not Trinitarian”
Your claim is that since the doctrine wasn’t in place, the faithful didn’t believe it. That is wrong. Doctrine didn’t establish this truth in the 4th or 5th century, but recognized something that existed all along in Christ’s Church.
The doctrine of the Trinity is encapsulated in Matthew 28:19, where Jesus instructs the apostles: “Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit.”
If that is true, please demonstrate homoousias from the scriptures.
That Christ is God is Supported in many Scriptures. Christ is not simply of similar essence.
Matt. 4:7; Luke 4:12 - Jesus tells satan, “you shall not tempt the Lord your God” in reference to Himself.
Matt. 9:2; Mark 2:5; Luke 5:20; 7:48 - Jesus forgives sins. Only God can forgive sins.
Matt. 12:8; Mark 2:28; Luke 6:5 - Jesus says that He is “Lord of the Sabbath.” He is the Lord of God’s law which means He is God.
Matt. 18:20 - Jesus says where two or three are gathered in His name, there He is in the midst of them.
Matt. 26:64; Mark 14:62; Luke 22:70 - Jesus acknowledges that He is the Son of God.
Matt. 28:20 - Jesus said He is with us always, even unto the end of the world. Only God is omnipresent.
Mark 14:36 - Jesus calls God “Abba,” Aramaic for daddy, which was an absolutely unprecedented address to God and demonstrates Jesus’ unique intimacy with the Father.
Luke 8:39 - Luke reports that Jesus said “tell how much God has done for you.” And the man declared how much Jesus did.
Luke 19:38,40 - Blessed is He who comes in the name of the Lord. If these were silent, the very stones would cry out.
John 5:18 - Jesus claimed to be God. The Jews knew this because Jesus called God His Father and made Himself equal to God. This is why Jesus was crucified.
John 5:23 - Jesus equates Himself with the Father, “whoever does not honor the Son does not honor the Father who sent Him.”
John 6:38 - Jesus says, “For I have come down from heaven.”
John 8:19 - Jesus says, “if you knew me, you would know my Father also.”
John 8:23 - Jesus says that He is not of this world. Only God is not of this world.
John 8:58 - Jesus says, “Before Abraham was, I AM.” Exodus 3:14 - “I AM” means “Yahweh,” which means God.
John 10:18 - Jesus says He has the power to lay down His life and take it up again - Gal. 1:1 - God raised Jesus to life.
John 10:30 - Jesus says, “I and the Father are one.” They are equal. The Jews even claimed Jesus made Himself equal to God. Jesus’ statement in John 14:28, “the Father is greater than I,” cannot contradict John 10:30 (the Word of God is never in conflict). Jesus’ statement in John 14:28 simply refers to His human messianic role as servant and slave, which He, and not the Father or the Holy Spirit, undertook in the flesh.
John 10:36 - again, Jesus claims that He is “the Son of God.”
John 10:38; 14:10 - “the Father is in me and I am in the Father” means the Father and Son are equal.
John 12:45 - Jesus says, “He who sees Me sees Him who sent Me.” God the Father is equal to God the Son.
John 13:13 - Jesus says, “You call me Teacher and Lord and you are right for so I AM.”
John 14:6 - Jesus says “I am the way, and the truth and the life.” Only God is the way, the truth and the life.
John 16:15 - Jesus says, “all things that the Father has are Mine.” Jesus has everything God has which makes Him God.
John 16:28 - Jesus says that “He came from the Father and has come into the world.”
John 17:5,24 - Jesus’ desire is for us to behold His glory which He had before the foundation of the world.
John 20:17 - Jesus distinguishes His relationship to the Father from our relationship by saying “My Father and your Father.”
Rev. 1:8 - God says He is the “Alpha and the Omega.” In Rev. 22:13, Jesus also says He is the “Alpha and Omega, the First and the Last, the beginning and the end.” The only possible conclusion one can reach is that Jesus is equal to the Lord God.
Rev. 1:17 - Jesus says again, “I am the First and the Last.” This is in reference to the God prophesied by Isaiah in Isaiah 44:6, 41:4, 48:12.
Rev. 2:8 - Jesus again says, “The words of the First and the Last, who died and came to life.” When did God die and come to life? In our Lord and Savior Jesus Christ.
**
Also, the Chruch Fathers:**
Ignatius of Antioch
“[T]o the Church at Ephesus in Asia . . . chosen through true suffering by the will of the Father in Jesus Christ our God” (Letter to the Ephesians 1 [A.D. 110]).
“For our God, Jesus Christ, was conceived by Mary in accord with God’s plan: of the seed of David, it is true, but also of the Holy Spirit” (ibid., 18:2).
Justin Martyr
“We will prove that we worship him reasonably; for we have learned that he is the Son of the true God himself, that he holds a second place, and the Spirit of prophecy a third. For this they accuse us of madness, saying that we attribute to a crucified man a place second to the unchangeable and eternal God, the Creator of all things; but they are ignorant of the mystery which lies therein” (First Apology 13:5–6 [A.D. 151]).
Theophilus of Antioch
“It is the attribute of God, of the most high and almighty and of the living God, not only to be everywhere, but also to see and hear all; for he can in no way be contained in a place. . . . The three days before the luminaries were created are types of the Trinity: God, his Word, and his Wisdom” (To Autolycus 2:15 [A.D. 181]).