The answer
He was called “The Prophet” and not “a prophet.” His prophetic work is to grant His people the spirit of prophesy (Rev. 19:10) or the revelation of the future life in heaven. The work of the prophets in the Old Testament was to lead the people to accept the person of the Messiah, who alone is able to carry them within Him, sanctify them, and enlighten their discernment, so they may come to know surpassing divine love.
St. John Chrysostom says, “For they hoped that a certain pre-eminent prophet would come, because Moses had said: ‘A prophet like me will the Lord, your God, raise up for you from among your own kinsmen; to him you shall listen’ (Deut. 18:15). But this Prophet was the Christ. For this reason they did not say: ‘Are you a prophet?’—inferring ‘one of many.’ But they used the article, ‘Are you the Prophet?’ [John 1:21]—that one, they meant, who was foretold by Moses. Thus it was that he denied, not that he was a prophet, but that he was that Prophet.”778
Fr. Tadros Yacoub Malaty
Notes
778 St. John Chrysostom, Homilies on John Homily 16 (John 1:19–27) (FOTC 33:154).