My Lord and my God. First testimony to the Deity of the risen Lord. Possibly Thomas was using the words of Psalms 86:15, which in the Septuagint read Kurie ho Theos, and claiming forgiveness for his unbelief on the ground of Exodus 34:6, to which this verse of the Psalm refers.
Related Commentaries of John 20:28
John 20:28
28 And Thomas answered and said unto him, My Lord and my God.