Leviticus 21:4

The husband shall not defile himself on account of his wife, except so far as it is right for him; but for a relative of those who do the work of his people he may defile himself.

Thus, a master may not defile himself for his household whether his people be kohanim or ordinary Israelites, except for the abovementioned relatives. and thereby become unholy This is an infinitive of the nif‘al form. The lamed acquires a dagesh because it absorbs a second lamed .

לא יטמא בעל בעמיו, no husband among the tribe of the priests is to defile himself ritually

להחלו, as he would thereby desecrate his status as a priest. According to the words of our sages (compare Rashi) he is not to so defile himself if his dead wife had been someone whom a priest should not have married in the first place, such as a divorcee; however, he is entitled or obligated to defile himself for the sake of burying a wife whom he was legally entitled to have married.

לא יטמא בעל בעמיו להחלו, the reason why a priest is not to defile himself through contact with the dead except those of his next of kin, is that also the priest is indeed a בעל בעמיו, a distinguished, highly placed member of his people, it is his task to understand and teach these laws as we know from Maleachi 2,7 “for the lips of the priest are meant to guard knowledge, and Torah and the people will enquire concerning these from his mouth.” This makes him a person to be treated in the manner one treats a politically highly placed person, a king. Seeing he is supposed to be ever ready to serve the King of Kings, in His Temple, it is not appropriate for such a person to desecrate his status even temporarily in order to participate in the burial rites of ordinary people. According to our sages in Sanhedrin 47 the prime purpose of burying and eulogising the dead is to render honour to them. This conflicts with the honour the priests have to accord to G’d on an ongoing basis. However, the Torah exempts the priests from this restriction for burial and eulogising of near relatives from this rule. [some of the last line is my own wording, though it corresponds to the thoughts expressed by the author. Ed.]

לא יטמא בעל בעמיו להחלו, “a husband [a priest, of course, Ed.] among his people, shall not contaminate himself to one (his wife) who had become his wife as a result of her having desecrated him.” According to the author of b’chor shor, we must understand this as if the Torah had written: לבעל בעמיו, even if he is a High Priest.” [The word בעל is being used by that commentator as “the highest authority,” not only the husband, i.e. his wife’s authority. Ed.] Even in the situation described, an alternate priest who is not allowed to defile himself except to the relatives mentioned in our portion may not substitute for the High Priest to save him from performing the commandment of מת מצוה.