Some awareness of Old Testament law is needed to understand the situation of Joseph in discovering the pregnancy of Mary. By law he was considered the husband of Mary as the result of their betrothal, even though he had yet to take her into his home.
Deuteronomy directs what is to be done if a betrothed woman has relations with another man. She is to be stoned unless she was raped.
Joseph was a just, righteous man. He was concerned with doing the right thing. Mary was obviously with child. Knowing Mary, he could not believe her blameworthy. He could think, says Jones, only of some unknown, perhaps supernatural cause.
He would not subject Mary to some procedure before a village court. He would divorce her quietly—perhaps without offering any specific reason as far as the public was concerned.