But the narratives of the incident near Caesarea Philippi which occurred at this crisis [MATTHEW 16:13-23] are asserted to be inconsistent with the truth of the accounts of earlier announcements of His Messiahship by Jesus, and recognition of Him as Messiah by His disciples. It is urged that if it had already before been declared to St. Peter that Jesus was the Christ and confessed by him and others, such an ardent blessing could not on this later occasion have been pronounced upon his faith; and more especially that the words could not have been used, "Flesh and blood hath not revealed it unto thee, but My Father which is in heaven" (MATTHEW 16:17). I believe, however, that we shall not think that there is any great inconsistency, if we endeavor to enter with a true historical imagination into the circumstances of the time at which St. Peter's Confession was made and take due account of common characteristics of the human mind.
The nature of the crisis I have already briefly indicated. The effects of our Lord's Galilean ministry had already developed themselves. The saying was being proved true there, as it was to be in still more awful form at Jerusalem, "For judgment came I into the world" (JOHN 9:39). The most diverse opinions about Him had become rife; on all hands the greatest perplexity had been caused by His words and conduct; men whose patriotic and other hopes had been stirred had now fallen away; the most part even of His disciples were keenly disappointed, and many who once followed Him went no more with Him (JOHN 6:66-67). The same national prejudices and other causes of perplexity which were felt by the Jews generally, affected all the minds of St. Peter and the rest of the Twelve. The very fact that so many were turning back would in itself be a trial of their faith.
Moreover, because once and again the conviction had flashed upon their minds before, that some utterance of Jesus or some great work implied that He was the Christ, it does not follow that they should be able to retain this conviction always. We know with what difficulty the mind really familiarizes itself with any new and great truth, and how hard it is to keep hold of any spiritual truth whatsoever, amid the thronging impressions of sense. We have had in some hour of great need, perhaps, or perhaps of exceptional calm and stillness, an overwhelming conviction of the certainty of some such truth. But as days and months filled with the ordinary occupations of life pass by, the impression of it fades, and we find ourselves not merely forgetting it, but even doubting its reality. The very fact, too, that Jesus had not since become more explicit, and had done and said many things which to the Twelve, not less than other Jews, would seem inconsistent with His being the Messiah, and even like an express resistance to such a view on His own part, would be calculated to make them doubt what they had believed before. To be able then, under such circumstances, to say with utmost seriousness and ardour of conviction, "Thou art the Christ," meant infinitely more than when such words were uttered in the first glow of hope and enthusiasm, or under the influence of a sudden relief from the peril of the storm. And it is not strange that it should be attributed to a special spiritual enlightenment and receive a peculiar blessing.
from pager 280-282, The Jewish and the Christian Messiah