That the High Priest shall not cohabit with a widow, even without marriage, because he profanes her, and it is said, “Neither shall he profane his seed among his people” (ibid. 21:15). He is thus prohibited from profaning one who would be eligible to be married to a priest

Leviticus 21:15

KJV

Neither shall he profane his seed among his people: for I the LORD do sanctify him.

ASV

And he shall not profane his seed among his people: for I am Jehovah who sanctifieth him.

WEB

He shall not profane his offspring among his people, for I am the LORD who sanctifies him.’”

JPS

And he shall not profane his seed among his people; for I am the LORD who sanctify him.