4 Now the angel having thus appeared, talks not with Mary, but with Joseph; and what says he? “Arise, and take the young Child and His mother.” Here, he says not any more, “your wife,” but “His mother.” For after that the birth had taken place, and the suspicion was done away, and the husband appeased, thenceforth the angel talks openly, calling neither child nor wife his, but “take the young Child and His mother, and flee into Egypt;” and he mentions the cause of the flight: “For Herod,” says he, “will seek the young Child's life.”
Joseph, when he had heard these things, was not offended, nether did he say, “The thing is hard to understand: Did you not say just now, that He should save His people?' and now He saves not even Himself: but we must fly, and go far from home, and be a long time away: the facts are contrary to the promise.” Nay, none of these things does he say (for the man was faithful): neither is he curious about the time of his return; and this though the angel had put it indefinitely thus: “Be there until I tell you.” But nevertheless, not even at this did he shudder, but submits and obeys, undergoing all the trials with joy.
And this because God, who is full of love to man, did with these hardships mingle things pleasant also; which indeed is His way with regard to all the saints, making neither their dangers nor their refreshment continual, but weaving the life of all righteous men, out of both the one and the other. This very thing He did here also: for consider, Joseph saw the Virgin with child; this cast him into agitation and the utmost trouble, for he was suspecting the damsel of adultery. But straightway the angel was at hand to do away his suspicion, and remove his fears; and seeing the young child born, he reaped the greatest joy. Again, this joy no trifling danger succeeds, the city being troubled, and the king in his madness seeking after Him that was born. But this trouble was again succeeded by another joy; the star, and the adoration of the wise men. Again, after this pleasure, fear and danger; “For Herod,” says he, “is seeking the young Child's life,” and He must needs fly and withdraw Himself as any mortal might: the working of miracles not being seasonable as yet. For if from His earliest infancy He had shown forth wonders, He would not have been accounted a Man.
Because of this, let me add, neither is a temple framed at once; but a regular conception takes place, and a time of nine months, and pangs, and a delivery, and giving suck, and silence for so long a space, and He awaits the age proper to manhood; that by all means acceptance might be won for the mystery of His Economy.
“But wherefore then,” one may say, “were even these signs wrought at the beginning?” For His mother's sake; for the sake of Joseph and of Simeon, who was presently to depart; for the sake of the shepherds and of the wise men; for the sake of the Jews. Since they, had they been willing to mind diligently what was taking place, would from this event also have reaped no small advantage in regard of what was to come.
But if the prophets do not mention what relates to the wise men, be not troubled; for they neither foretold all things, nor were they silent touching all. For as without any warning to see those things coming to pass, would naturally occasion much astonishment and trouble; so also to have been informed of all would dispose the hearer to sleep, and would have left nothing for the evangelists to add.
Source: Homilies on the Gospel of St. Matthew (New Advent)