John 20:28 - Coke's Commentary on the Holy Bible

Thomas answered and said, &c.— Though the nominative often occurs for the vocative, it is the former case which is used here, the words συ ει, thou art, being understood. To this the context agrees; for we are told that these words were addressed to Jesus; wherefore they cannot be taken merely as an exclamation of surprise, which is the Socinian gloss; but their meaning is, "Thou art really he whom I lately followed as my Lord; and I confess thee to be possessed of infinite knowledge, and worship thee as my God." It is not fair that Thomas actually touched our Lord's wounds; and Christ himself says afterwards, John 20:29 that his belief was built on sight; which, though it does not exclude any evidence that might have been afforded the other senses, yet seems to intimate, that this condescension of our Lord, together with the additional evidence arising from the knowledge that he plainly had of that unreasonable demand which Thomas had made in his absence, with divine grace accompanying the whole, quite overcame him.