But when he thought this, behold, an angel of the Lord appeared to him in a dream, saying:

When the righteous man hesitated, an angel appeared, teaching him what he should do. He appears to him in a dream because Joseph had strong faith. The angel spoke to the shepherds as if they were rude in reality, but to Joseph, as if he were righteous and faithful, in a dream. How could he not believe when the angel taught him what he had been talking to himself about and what he had told no one? As he pondered, but spoke to no one, an angel appeared to him. Of course, Joseph believed that this was from God, for only God knows the ineffable.

Joseph, son of David.

He called him the Son of David, reminding him of the prophecy that Christ would come from the seed of David. As the angel said this, he urged Joseph not to believe, but to think of David, who had received the promise concerning Christ.

Don't be afraid to accept.

This shows that Joseph was afraid to have Mary, so as not to offend God by protecting an adulteress. Or in other words: "Do not be afraid," that is, be afraid to touch her, as having conceived of the Holy Spirit, but "do not be afraid to receive," that is, to have her in your home. For in mind and thought Joseph had already dismissed Mary.

Mary, your wife.

It is the angel who says: "Perhaps you think that she is an adulteress. But I tell you that she is your wife," that is, she is not corrupted by anyone, but your bride.

For that which is born in Her is of the Holy Spirit.

For not only is she far from being unlawfully mixed, but she has conceived in some divine way, so that you ought to rejoice the more.

She will give birth to a son.