LEV871 No Kohen shall marry an immoral woman. No Kohen Gadol or regular Kohen may marry a woman who has had intimate relations with a man who she is forbidden to marry. Similarly, if she had relations with a Kohen challal (חלל)--a Kohen who was forbidden to serve in the Sanctuary--no other Kohen may marry her. Key concepts: Hashem chose the Kohanim to serve Him in the Beis HaMikdash on a constant basis, so in many respects they must live on a higher plane of purity and sanctity than what is required of the rest of our nation. Since a man's wife is often on his mind, the Torah forbids any Kohen to marry a woman who has an evil nature and immoral character, lest she corrupt him and cause him to deviate from the correct path. In addition, anyone who becomes close to such a woman bring shame and disgrace upon himself, for everyone scorns and derides her.