Joseph was a just man. In the Bible, as consequently in our Christian life, the justice which matters most is never any mere human social or political justice but only the justice of God. Joseph's justice, as well as his relationship with Mary, is only known to us from Scripture. The Word of God, is therefore revealed to us only as part of the mystery of the Incarnation.

A first superficial and common notion is that Matthew accepted that Joseph was just with respect to the law of Moses, which seemed to demand that, not knowing how Mary came to be pregnant, he should divorce Mary, but being a kindly man he decided to do this "quietly" or secretly. This notion, however, is not adequate or commensurate with the whole atmosphere of holiness and divine mystery which pervades the whole Gospel account.

A more reasonable explanation is that Joseph was a holy man, sensitive to the presence of God and this would have naturally led him to the realization that somehow Mary's situation was the work of God and that he should withdraw so as not to interfere with God's work.