HOMILY OF ST JEROME, PRIEST
(Book 1 of Commentary on Matthew, Ch.1)
Why was he conceived of a betrothed virgin, rather than of one who was free? First, that through the genealogy of Joseph, the lineage of Mary might be shown. Secondly, lest she should be stoned by the Jews as an adulteress. Thirdly, that she might have a comforter when fleeing into Egypt. The Martyr Ignatius even added a fourth reason why he should have been conceived of a betrothed virgin: “That his birth,” he says, “might be concealed from the devil, since he would suppose that he had been born, not of a virgin, but of a married woman.
Joseph kept silence about the mystery he did not understand
But Joseph, her husband, being a just man and not wishing to expose her to reproach, was minded to put her away privately. If anyone is joined to an adulteress, he becomes one body with her, and according to the Law, not only those who commit such sin but also those who have knowledge of it, are held guilty. How then could Joseph be described as just if he had concealed the sin of his wife?
But it is a testimony to Mary that Joseph, knowing her chastity, yet wondering what had happened, kept silence about the mystery he did not understand.