Matthew tells us Joseph was “righteous.” Which means, being a good Jew, that he was righteous before not only God, but the Law.
This is significant, because Joseph, in the story Matthew goes on to tell, doesn’t follow the letter of the Law. In fact, he subverts it, “unwilling,” Matthew writes, “to expose her to shame.” You see, if Joseph exposed her, suggesting she may have committed adultery, she could have been killed. Such was the Law. But Joseph keeps quiet. He doesn’t put her life at risk. Further, he subverts social pressure and convention—somewhat!—by trying to divorce her quietly. He’s not all that afraid of what people will think of him. Instead, his concern is to do the right thing: not to put Mary in harm’s way and simply cut his losses with a simple divorce.
But then comes the angel and the divine message. Mary will bear the Christ, and you, Joseph, are to serve as his father. Proven a good man, that’s what he hears. Joseph, the righteous man, is now recruited as an agent of divine redemption. Because that’s the sort of man God was looking for—righteous in a Joseph sort of way.
And so, the lesson is simple: be like Joseph. Be righteous in the ways of God, but don’t twist God’s law in such a way that you cause harm. And also, don’t give in to social pressure! Do right and fear no one. But then, also be open to the divine and the words of angels. Be open to God. Because that’s how you’ll know what God wants you to do, how you’ll know how to be useful in God’s redeeming of the world.