Commento su Levitico 21:15

ולא יחלל זרעו NEITHER SHALL HE PROFANE HIS SEED — ,thus if he marries one of these women disqualified for a union with him his offspring (זרעו) from her becomes “profaned" (חלל) being exempted from the general law of holiness that applies to the priestly status (cf. Kiddushin 77a).

AND HE SHALL NOT PROFANE HIS SEED AMONG HIS PEOPLE. “Thus if he married one of these women who are disqualified for him, his offspring from her becomes profaned [i.e., disqualified] from the law of the sanctity of the priesthood.” This is Rashi’s language.
The Rabbi [Rashi] thus explained the verse [before us] as a mere negation, meaning: “these shall he not take in order that he profane not his offspring.” But in the opinion of our Rabbis, this constitutes a second negative commandment. Thus they have said:⁵⁴Kiddushin 78 a. “If [a High Priest or a common priest] betrothed and had intercourse with one of the women disqualified to him, he is subject to two penalties of whipping, once on account of he shall not take, and again on account of he shall not profane.” And the Rabbis have also said there: “If he has intercourse without betrothal, he is liable to whipping on account of he shall not profane.” Thus it is clear that these are two negative commandments. They have also explained there the reason why, for [mere] betrothal without [subsequent] intercourse, he is not liable to whipping, because [Scripture says: he shall not take … he shall not profane, meaning:] Why must he not take [her as his wife]? “In order that he may not profane” [his offspring, and therefore if the marriage was not consummated, and he can have no offspring from her, he is not liable merely for the betrothal]. If so, the meaning of the expression, these shall he not take, is “because I [the Eternal] admonish him against profaning his seed,” and from this statement we ourselves deduce that his offspring from one of the disqualified women is profaned, [rendered unfit for the priesthood].

ולא יחלל, “so that he will not desecrate, etc.” Rashi understands the message of our verse, as “he must not take as a wife someone forbidden to him so that he will not desecrate any male children he will have from such a union.” Nachmanides rejects this interpretation saying that if it were correct our verse is not a negative commandment, but merely an explanation of the legislation. Our sages (Kidushin 78) make plain that our verse is an additional negative commandment, i.e. a priest will receive twice 39 lashes for what might have a appeared as violating a single commandment. In fact he violates לא יקח as well as לא יחלל.

Profaned from the status of the holiness of the kehunoh. I.e., his male children are permitted to become impure, to marry a divorcee, and anything similar. (Nachalas Yaakov)

ולא יחלל זרעו, “so that he will not profane his seed,” by marrying these profaned people secretly.”