"u'Shemartem es Mishmarti". Having already issued the Mitzvah of Shemirah (guarding against sinning - in Pasuk 26), why does the Torah repeat it here?
Rashi #1: To warn Beis-Din to see to it that the laws of Arayos are adhered to. 1
Rashi (in Beitzah, 2b): To teach us the implication to make a Mishmeres for the Mitzvos, but not for a Mishmeres ? from which Chazal extrapolate 'Ein Osin Gezeirah li'Gezeirah'.
Seforno and Targum Yonasan: The Torah is warning us here that in order to avoid contaminating ourselves, we should take care to observe even the Mitzvos that Hashem commanded as a Geder (a fence against sinning). 2
Mo'ed Katan, 5a: It is a hint that one should msark graves ? to avoid the KOhanim becoming Tamei. 3
Having stated "Ani Hashem Elokeichem" at the beginning of the Parshah, why does the Torah repeat it here?
Rashi: To stress that Hashem is only our G-d as long as we do not contaminate ourselves with the above-mentioned sins; because if we do, we will disqualify ourselves from His jurisdiction and bring destruction upon ourselves.