Matthew 16:20

When the disciples had received the Spirit, then the teaching concerning the divinity of the Son was shown to them perfectly and the Spirit himself bore witness through the miracles that were done in his name. Yet it was still necessary that this be hidden …

(Verse 20) Then he commanded his disciples not to tell anyone that he was Jesus Christ. Before sending the disciples to preach, he had ordered them to announce his coming: here he instructed them not to say that he was Jesus Christ. It seems to me that preaching Christ is one thing, and preaching Jesus Christ is another. Christ is a common name of dignity: Jesus is the proper name of the Savior. However, it may be that before his passion and resurrection, he did not want to be preached; but after the completion of the sacrament of his blood, he would more fittingly say to the apostles: Go, teach all nations (Matthew last chapter, verse 19), etc. So that no one thinks that our intelligence alone, and not the Gospel teachings that follow, explain the reasons for the prohibition of preaching at that time.

For what having once had root has afterwards been torn up, if it is again planted, is with difficulty retained among the multitude; but what having been once rooted has continued ever after unmoved, is easily brought on to a further growth. He therefore dwells on these sorrowful things, and repeats His discourse upon them, that He may open the minds of His disciples.

And then, when He had so said, "He charged them that they should tell no man that He was the Christ." And why did He charge them? That when the things which offend are taken out of the way, and the cross is accomplished, and the rest of His sufferings fulfilled, and when there is nothing any more to interrupt and disturb the faith of the people in Him, the right opinion concerning Him may be engraven pure and immovable in the mind of the hearers. For, in truth, His power had not yet clearly shone forth. Accordingly it was His will then to be preached by them, when both the plain truth of the facts, and the power of His deeds were pleading in support of the assertions of the apostles. For it was by no means the same thing to see Him in Palestine, now working miracles, and now insulted and persecuted (and especially when the very cross was presently to follow the miracles that were happening); and to behold him everywhere in the world, adored and believed, and no more suffering anything, such as He had suffered. Therefore He bids them "tell no man." For that which hath been once rooted and then plucked up, would hardly, if planted, again be retained among the many; but that which, once fixed, hath remained immovable, and hath suffered injury from no quarter, easily mounts up, and advances to a greater growth. And if they who had enjoyed the benefit of many miracles, and had had part in so many unutterable mysteries, were offended by the mere hearing of it; or rather not these only, but even the leader of them all, Peter; consider what it was likely the common sort should feel, being first told that He is the Son of God, then seeing Him even crucified and spit upon, and that without knowledge of the secret of those mysteries, or participation in the gift of the Holy Ghost. […]

Seeing Peter had confessed Him to be Christ the Son of the living God, because He would not have them preach this in the mean time, He adds, Then charged he his disciples that they should tell no man that he was Jesus the Christ. Or they then spake of Him in lowly words, as only a great and wonderful man, but as yet proclaimed Him not as the Christ. Yet if any will have it that He was even at the first proclaimed to be Christ, he may say that now He chose that first short announcement of His name to be left in silence and not repeated, that that little which they had heard concerning Christ might be digested into their minds. Or the difficulty may be solved thus: that the former relation concerning their preaching Christ does not belong to the time before His Resurrection, but to the time that should be after the Resurrection; and that the command now given is meant for the time present; for it were of no use to preach Him, and to be silent concerning His cross. Moreover, He commanded them that they should tell no man that He was the Christ, and prepared them that they should afterwards say that He was Christ who was crucified, and who rose again from the dead.