One of the themes in St. Mark’s gospel is that Jesus tried to lead his disciples step by step to an acknowledgement of his divine Sonship. As a result, Mark takes pains to show that Jesus, during his earthly life, did not openly declare from the first moment of his ministry who he really was; the full revelation first moment of his ministry who he really was; the full revelation had to wait until Jesus had shown the meaning of his mission by suffering and dying. This is certainly Mark’s theory; was it the common belief of the early Church, and if so, does it represent what really happened?
That it is Mark’s theory needs little proof. According to Mark, Jesus forbade the unclean spirits to reveal who he was (Mk 1:34; 3:12); he imposed the same prohibition on those whom he cured by astounding miracles (1:44; 5:43; 7:36; 8:26), and even on the disciples (8:30; 9:9). Mark tells how the disciples did not really understand the truth about the personality of Jesus (4:41; 6:51-52; 8:16-21; 9:33-34; 10:35, 41-42) and implies that half the purpose of speaking in parables was to conceal the mystery from those who were unworthy to know it (4:11). Matthew has no parallel to most of these texts (only to Mk 8:30 and 9:9), and even though he has one text not in Mark which teaches the same lesson (Mt 9:30), as a general rule he plays down the lack of understanding shown by the disciples. Luke also plays down the disciples’ lack of understanding, and he never mentions that Jesus forbade them to speak about his messianic mission. For these reasons, many scholars claim that the theory of the ‘messianic secret’ is a purely Markan invention.
At first sight, it looks as if Mark did invent this theory; but there is one objection. Mark has included in his gospel two passages (Mk 2:10, 28; 10:47-52) in which Jesus apparently did not order men to refrain from broadcasting his identity. Mark presumably took these texts from his sources without altering them; and therefore it may have been Mark’s fidelity to his sources which led him to state so frequently that Jesus forbade men to tell everyone who he was. In that case, the ‘messianic secret’ would not have been Mark’s invention but a datum of very old tradition. Matthew, as we have seen, is less scrupulous in the treatment of his sources, and therefore it is more likely that he suppressed it (particularly in the light of his theology); in one text, though, he has preserved an example of the same tradition which is not recorded by Mar (Mt 9:27-31), and which therefore cannot have been based on Mark.
The theme of the ‘messianic secret’ is therefore not something thought up by Mark, but a datum which Mark accepted from tradition. Matthew transposed the idea and presented it as the story of Jesus’ withdrawal from public preaching (Mt 12:15-21; 14:1-16:12); John has transposed the idea in a different way by presenting his dialogues as questions addressed to the reader. Thus the common tradition underlying the gospels shows Jesus not merely as a Messiah who was in fact unknown, but as one who himself chose to conceal his identity. (Xavier Léon-Dufour, The Gospels and the Jesus of History [trans. John McHugh; London: William Collins Sons & Co. Ltd, 1968], 232-33)