Or HaChaim on Leviticus 18:26/אור החיים על ויקרא י״ח:כ״ו

1 ועמדתם אתם, "and you shall observe, etc." The reason the Torah uses the word אתם, "you," after having already addressed the people as "you" by addressing them directly is, that this commandment is intended as a warning that the various statutes and ordinances not be disregarded by all the people who have been commanded to observe them. A person should not say that his only concern is that he personally should not be the cause of the particular commandment being ignored. By saying ושמרתם את חקותי, the Torah imposes upon each one of us the obligation to see to it that others observe these statutes. Seeing that such an obligation devolves only on the people with influence on the people, i.e. Moses and his court, the Torah added the word אתם to make sure that we understood who was being addressed here. It is the function of a Jewish court to ensure that the people observe G'd's commandments. In Torat Kohanim our sages said that the reason that Moses and his court are being charged with that responsibility is that they themselves were already in the habit of observing these commandments. This made them a natural for supervising observance of these laws by the whole nation. We have a similar approach to Song of Songs 4,12: גן נעול אהותי כלה גל נעול מעין חתום. "A garden locked up is my sister, a spring locked up a fountain sealed." Solomon used a well understood hyperbole to describe chaste behaviour by the Jewish people. The message is that the legislation about sexual prohibitions is not something new and strange to the Jewish people but that they had always excelled in chastity as part of their nature. The Torah may have alluded to this by reminding the people with the word אתם, i.e. "something that you are already used to."

2האזרח והגר, "the natural-born Jew as well as the proselyte." Torat Kohanim explains that were it not for the extra letter ה at the beginning of the word אזרח I would have interpreted these laws as applying only to the males. The same is true about the letter ה at the beginning of the word הגר. As it is, the laws also apply to the wives of the natural-born Jews as well as to the wives of the proselytes. Thus far Torat Kohanim. The only reason that the Torah had to write something at all in order to include the women is the word אתם which is clearly masculine.

3Another reason the Torah even mentions the proselytes is to tell us that if both the Israelites and the proselytes will adhere to these regulations on sexual chastity, then the deviations practiced by the local population will lose the power to make the land spew out its inhabitants. The tendency of the land to do this was limited to the period prior to the Israelites occupying it. In other words, it is entirely up to Israel and the proselytes if the land will or will not spew out its inhabitants.

4You are no doubt aware of Exodus 23,33 in which the Torah warns not to conclude any treaties with the local inhabitants of the land of Canaan as they are apt to persuade you to sin against G'd. Maimonides as well as the author of the Semak remark that a Gentile who fails to observe the seven Noachide laws is not even allowed to dwell in the land of Israel for this very reason. This teaches you that if it had not been for their failure to accept the Noachide laws the land would not have spewed out anybody on their account. [Many of the prohibitions in our chapter do not form part of the Noachide laws. Ed.]