Jamieson, Fausset and Brown on Matthew 16:15

15. He saith unto them, But whom--rather, "who."

say ye that I am?--He had never put this question before, but the crisis He was reaching made it fitting that He should now have it from them. We may suppose this to be one of those moments of which the prophet says, in His name, "Then I said, I have labored in vain; I have spent my strength for naught, and in vain" (Is 49:4): Lo, these three years I come seeking fruit on this fig tree; and what is it? As the result of all, I am taken for John the Baptist, for Elias, for Jeremias, for one of the prophets. Yet some there are that have beheld My glory, the glory as of the Only-begotten of the Father, and I shall hear their voice, for it is sweet.