John Calvin Commentary Leviticus 21:7

"They shall not take a woman that is a harlot, or profane; neither shall they take a woman put away from her husband: for he is holy unto his God." — Leviticus 21:7 (ASV)

They shall not take a wife. The third kind of purity is in marriage itself, so that the priests’ home may be chaste and free from all dishonor. God also commands at this time through Paul that pastors should be chosen who rule their own houses well, whose wives are chaste and modest, and their children well-behaved (1 Timothy 3:2; Titus 1:6).

The same reason for this existed under the Law, so that those appointed for the government of the Church would not be despised and looked down upon because of their domestic vices.

But God especially regarded the priesthood of Christ, so that it would not be exposed to contempt. It was indeed permitted that men could marry without penalty a woman divorced from her husband, though in the sight of God such a union was unlawful. No law forbade private individuals from marrying a woman who was not a virgin; but what was permitted to the general populace, God condemned in the priests, to keep them from any mark of disgrace.

This reason is also expressed when God says that He desires the priests to be holy, because He has chosen them for Himself. For if the people had not respected them, all religion would have been held in contempt.

Therefore, to preserve their dignity, God commands them to take great care not to expose themselves to disgrace. Finally, to further emphasize the reverence for their holy office, He reminds them that it related to the welfare of the whole people, for God says, “I the Lord do sanctify him” (Leviticus 21:15).

In these words He suggests that the grace of adoption, by which they were chosen as His heritage, was based on the priesthood.