In the Gospels, Jesus asks His disciples who they think He is, and Peter responds by confessing that He is "the Christ, the Son of the living God", probably using these as co-referring terms (Matthew 16:13-17, Mark 8:27-29, Luke 9:18-20, compare John 6:67-69):
Matthew 16:13-17
13 When Jesus came into the coasts of Caesarea Philippi, he asked his disciples, saying, Whom do men say that I the Son of man am?
14 And they said, Some say that thou art John the Baptist: some, Elias; and others, Jeremias, or one of the prophets.
15 He saith unto them, But whom say ye that I am?
16 And Simon Peter answered and said, Thou art the Christ, the Son of the living God.
17 And Jesus answered and said unto him, Blessed art thou, Simon Barjona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven.
Above, notice that Jesus is pleased with his answer, and says that Peter is blessed, in that it was revealed to him by God.
Consider this confession, and what it signifies about the beliefs of Peter. Suppose he were to believe that Jesus was God, as Trinitarianism teaches. In that case, he would not waste a moment confessing that Jesus is the "anointed of God" (Christ), or "Son of God", but rather, would exclaim something like, "You are God, the maker of all things". If one believes that God is walking around in their midst, how could any person fail to mention as much, when asked by their God incarnate who they say He is? Yet, Peter does not do this, because he does not believe that Jesus is God, but rather, the Messiah of God.
And, there is no indication that Peter ever changed his confession, or augmented it to include more than Jesus had commended him for at the coasts of Caesarea Philippi. When he stands up to preach in the book of Acts, his preaching lacks a mention of Jesus's alleged Deity entirely, while communicating to any ordinary listener that Jesus is distinct from God, and is not God (Acts 2:22, 2:36, 3:13, 3:26, 4:10, 5:30-31, 10:38-42).
For instance:
Acts 2:36
36 Therefore let all the house of Israel know assuredly, that God hath made that same Jesus, whom ye have crucified, both Lord and Christ.
As in his confession, if Peter had intended at all to communicate that Jesus is God, the above would be antithetical to his cause. He says that "God" (subject one) made "Jesus" (subject two), "both Lord and Christ". The ordinary, unconverted Jew who he was preaching to could not have failed to understand this to be saying that Jesus is distinct from God. And, it would have required them to ignore Peter's own words to get what is, from the Trinitarian perspective, a proper understanding of who Jesus was - God, allegedly. Such a doctrine cannot be gleaned from this text, because Peter did not believe in it.
So, where does that leave Peter's confession? In today's theological landscape, if a Unitarian were to make Peter's exact confession, as he intended it, standing in front of Jesus, we would be told by our Trinitarian brethren that there is far more - immeasurably more - that must be confessed, otherwise, our Christology is severely deficient. If a Unitarian stops where Peter's confession stopped, they are often accused of having denied Jesus, corrupted the Gospel, and deprived themselves of salvation. So, while every Trinitarian would acknowledge that Peter's confession of Jesus's identity as the Christ is true, they really believe that it is by itself woefully deficient, and lacking the most important aspect of Jesus's identity.
Because of the prestige of the doctrine of the Trinity, the confession of one of the closest followers of Jesus as to who He is can only be affirmed by most Christians with caveats - that Peter learned more later on, or stated more later on that he already knew, or that "Son of God" means "God the Son", or that "Christ" is a co-referring term for God - all of which read so much into such a simple, straightforward confession of faith. Peter never said those things, and neither do the Gospel writers, or anyone else in the New Testament. Instead, he contented himself with confessing that Jesus is the Christ, and Jesus accepted this, and praised him for it. Who, then, has the right to demand any more of anyone, when discussing the identity of Jesus?