The Gemara (Sukkah 40) discusses the harsh punishment that one incurs when he treats the laws of Shemittah lightly. The Gemara uses the term avak shel sheviis, the dust of Shemittah, to refer to the less stringent laws of Shemittah. We find elsewhere that the Gemara uses the term avak Lashon hara to describe slander that is rabbinically prohibited, and the term avak ribbis in describing rabbinically prohibited interest on a loan. Why does the Gemara use the word avak, dust, in these instances? It is noteworthy that when Yaakov struggled with the angel of Esav, it is said (Bereishis 32:25) vayeiavek ish imo, and a man wrestled with him. The Gemara in Chullin 91a states that the angel of Esav appeared to Yaakov like a Torah scholar. Perhaps the meaning of the Gemara is that the angel of Esav attempted to convince Yaakov that although one must follow the mitzvos that are stated explicitly in the Torah, one can be more lenient regarding the rabbinical prohibitions. This is alluded to in the word vayeiavek, which is derived from the word avak, dust. For this reason the Gemara refers to certain rabbinical prohibitions with the term avak, to allude to the idea that it is the evil inclination, a.k.a. the angel of Esav, who is attempting to convince the person that he can be lenient regarding rabbinical prohibitions. We must adhere to the dictum recorded in Pirkei Avos 1:4, where it is said vehevay misabak bafar ragleihem, literally translated as sit in the dust of their feet, and homiletically interpreted that one should adhere to even the less stringent rabbinical prohibitions.