Expositor's Bible Commentary Commentary Matthew 1:19

"And Joseph her husband, being a righteous man, and not willing to make her a public example, was minded to put her away privily." — Matthew 1:19 (ASV)

Joseph did not know about the visit of an angel to Mary, but it eventually became obvious that she was pregnant. Because he was a righteous man, he could not in conscience marry Mary, who was now thought to be unfaithful. Such a marriage would have been a tacit admission of his own guilt. But because he was unwilling to expose her to the disgrace of public divorce, Joseph therefore chose a quieter form of divorce, before two witnesses, permitted by the law itself. It would leave both his righteousness (his conformity to the law) and his compassion intact.