7 “And Joseph her husband, being,” says he “a just man, and not willing to make her a public example, was minded to put her away privily.”
Having said that it was of the Holy Ghost, and without cohabitation, he establishes his statement in another way again. Lest any one should say, “Whence does this appear? Who has heard, who has seen any such thing ever come to pass?”— or lest you should suspect the disciple as inventing these things to favor his Master;— he introduces Joseph as contributing, by what he underwent, to the proof of the things mentioned; and by his narrative all but says, “If you doubt me, and if you suspect my testimony, believe her husband.” For “Joseph,” says he, “her husband, being a just man.” By “a just man” in this place he means him that is virtuous in all things. For both freedom from covetousness is justice, and universal virtue is also justice; and it is mostly in this latter sense that the Scripture uses the name of justice; as when it says, “a man that was just and true;” and again, “they were both just.” Being then “just,” that is good and considerate, “he was minded to put her away privily.” For this intent he tells what took place before Joseph's being fully informed, that you might not mistrust what was done after he knew. However, such a one was not liable to be made a public example only, but that she should also be punished was the command of the law. Whereas Joseph remitted not only that greater punishment, but the less likewise, namely, the disgrace. For so far from punishing, he was not minded even to make an example of her. Do you see a man under self-restraint, and freed from the most tyrannical of passions. For you know how great a thing jealousy is: and therefore He said, to whom these things are clearly known, “For full of jealousy is the rage of a husband;” “he will not spare in the day of vengeance:” and “jealousy is cruel as the grave.” And we too know of many that have chosen to give up their lives rather than fall under the suspicion of jealousy. But in this case it was not so little as suspicion, the burden of the womb entirely convicting her. But nevertheless he was so free from passion as to be unwilling to grieve the Virgin even in the least matters. Thus, whereas to keep her in his house seemed like a transgression of the law, but to expose and bring her to trial would constrain him to deliver her to die; he does none of these things, but conducts himself now by a higher rule than the law. For grace having come, there must needs henceforth be many tokens of that exalted citizenship. For as the sun, though as yet he show not his beams, does from afar by his light illumine more than half the world; so likewise Christ, when about to rise from that womb, even before He came forth, shone over all the world. Wherefore, even before her travail, prophets danced for joy, and women foretold what was to come, and John, when he had not yet come forth from the belly, leaped from the very womb. Hence also this man exhibited great self-command, in that he neither accused nor upbraided, but only set about putting her away.
Source: Homilies on the Gospel of St. Matthew (New Advent)