Comentario sobre Levítico 18:30

ושמרתם את משמרתי THEREFORE SHALL YE KEEP (OR, WATCH OVER) MY CHARGE — This is intended to caution the court regarding this (Sifra, Acharei Mot, Chapter 13 22).

ושמרתם את משמרתי לבלתי עשות מחקות התועבות, observe also the legislation which is in the nature of a protective fence against the major sin of indulging in actual sexual relations with the forbidden partners. Just as the legislation governing menstrual laws, eating of forbidden foods, sleeping with a woman ritually impure after giving birth, etc., have all been surrounded with what our sages call a סיג, “protective fence,” this legislation too has such a protective fence which must not be ignored except at your peril. The overriding consideration is לא תטמאו בהם, “do not become spiritually contaminated by ignoring these laws.”

ושמדתם את משמדתי, "You shall observe My ordinance, etc." Here G'd issues a warning to observe the "security fence" erected by the sages so as to make it unlikely that one breaches one of the Biblical commandments concerning sexual mores. The word משמרת refers to such a "fence." The reason the Torah added the words לבלתי עשות, "not to do, etc," is to explain that the "fence" is designed to protect us from even inadvertently breaching the עריות legislation. Even though a person would not become guilty of the penalties provided for people who willingly violate the prohibitons in this chapter, they would still defile themselves. In order to avoid this, the Torah urges "observe My protective fence."