Trinitarians claim that Thomas himself is here identifying Jesus as "God" and they further claim that Jesus' response to Thomas confirms his words to Jesus that he is indeed "God."
Examination of the Claim
1. Thomas said these words to Jesus
The text plainly states that Thomas said these words directly to Jesus.
Thomas answered and said to Him, "My Lord and my God!"
2. The Immediate Context: Seeing and Believing
Both the preceding and following context concern seeing and believing.
Then He said to Thomas, "Reach here with your finger, and see my hands and reach here your hand and put it into my side; and do not be unbelieving, but believing. Thomas answered and said to Him, "My Lord and my God!" Jesus said to him, "Because you have seen me you have believed. Blessed are they who did not see and yet believed."
3. The Overall Context
The overall context militates against the Trinitarian claim where Jesus describes his Father as Mary's God, as opposed to himself, and John indicates that he writes this Gospel, including the account of Jesus and Thomas, not to tell us that Jesus is himself God but instead that Jesus is God's son:
We have seen the Lord. (20:25).
I ascend to my Father and your Father, and my God and your God. (20:17)
These things have been written so that you may believe that Jesus is the Christ, the Son of God and that believing you may have life in His name. (20:31).
Since John writes that we might have life believing in the name of Jesus, one should also be reminded of Jesus' words at John 17:3, "Father.... this is eternal LIFE that they may know You, the only true God, and Jesus Christ whom You sent."
4. The Greek Text
Thomas' words to Jesus in Greek literally read, "the Lord of me and the God of me." In Greek this is how one would refer to two persons. If one wanted to refer to one person he would say, "the Lord and God of me." This is confirmed by the first and Sixth Granville Sharp rules. However, Trinitarians make a convenient exception to the sixth rule for this particular verse.
There are actually TWO important things to see here. First, there is the fact that both nouns, (1) Lord, and (2) God, are each qualified by the definition article ('the'). Second, both nouns, (1) Lord, and (2) God, are qualified by the words "of me." This is also telling. Thomas could have said, "the Lord and the God of me." But he did not.
Analysis of the Evidence
1. The Granville Sharp First and Sixth Rules
The Granville Sharp First Rule of Greek Grammar states that when you have a TSKS construction, only one person is being identified. In simple terms, this means a THE-NOUN-AND-NOUN word construction. So if a person wanted to refer to Jesus as his Lord and God it would be stated in Greek as, "the Lord and God of me." Essentially, one definite article ("the") indicates one person is in view. Trinitarians insist upon this rule at Titus 2:13 and allow no one any exceptions. However, this is not the construction Thomas used at John 20:28. Thomas used the construction which Greek speakers used to refer to two persons.
The Granville Sharp first rule was the result of research by a man named Granville Sharp. However, it is not enough for someone to say that such a Greek construction demonstrated only one person is in view. He had to also demonstrate that a Greek speaker would say such words differently if two persons were in view instead of one.
The Granville Sharp Sixth Rule states that when you have a TSKTS construction, two persons are in view. In simple terms, this is a THE-NOUN-AND-THE-NOUN construction. So if you wanted to refer to both your Lord and another identity who is your God, you would say, "the Lord of me and the God of me." Essentially, two definite articles ("the") indicates two persons are in view. One definite article, one person, two definite articles, two persons. However, while Trinitarians allow no one any exceptions to the first GS rule at Titus 2:13, they completely deny the sixth GS rule at John 20:28 and make a convenient exception for themselves for the sake of their doctrine.
2. Further Grammar Observations
Thomas not only used the Greek convention to signify two persons, he also did something else which indicates two persons are being identified. Thomas also did not say, "the Lord and the God of me." He actually said, "the Lord OF ME and the God OF ME." This further indicates that Thomas had two persons in view.
3.The Grammar of the Context
At John 20:17, Jesus speaks and uses the Greek convention to signify one person, "THE Father of me and Father of you and God of me and God of you." This is even further evidence that Thomas did not refer to one person but to two persons. John's grammar convention is to use one definite article for one person as we see in John 20:17 only a few verses prior to John 20:28. The "of me" vs. "of you" expressions are simply alternating and contrasting ways necessary for Jesus to make his point.
4. What Jesus said about Seeing and Believing
The grammatical evidence that Thomas was referring to two persons is very weighty. So now we must inquire as to whether there is any other evidence this could be the case, especially from John's Gospel since John 20:28 appears in John's Gospel. And indeed, Jesus gives a very clear teaching that exactly pertains to our question.
We have seen that preceding verse and the following verse of John 20:28, the immediate context, is about seeing and believing. Thomas' statement is embedded and framed by Jesus' comments on seeing and believing. Jesus explained on at least two occasions what it means to see and believe in him - that to see and believe in him was to see and believe in the Father.
And Jesus cried out and said, "He who believes in Me does not believe in Me but in Him who sent Me. He who sees Me sees Him who sent Me." (John 12:44-45).
He who has seen Me has seen the Father. (John 14:9).
My Lord and My God. (John 20:28).
Keeping in mind that John 20:28 is embedded and framed in Jesus' statements about seeing and believing, carefully regard what Jesus taught us with respect to John 20:28.
||He who BELIEVES in ME
||[BELIEVES] in HIM who sent me.
|| He who SEES ME
||SEES HIM who sent me
||He who has SEEN ME
||has SEEN THE FATHER.
||and MY GOD.
When all the evidence is weight, there is simply no doubt that Thomas was affirming Jesus' earlier teaching to him and the other disciples, that to see and believe in Jesus was to see and believe in the Father.