What are the implications of "Ki Lo Davar Reik Hu Mikem' "?
Rashi #1: It implies that he does not toil over the words of Torah in vain, but they earn one a great reward - in fact they are the very source of life.
Rashi #2: There is nothing in the Torah that is not subject to reward for expounding it. 1
Targum Yonasan: There is nothing empty in the Torah
Rashi: Proof of this lies in the seemingly 'empty' Pesukim "va'Achos Lotan Timna" (Bereishis 36:22) and "ve'Timna Haysah Pilegesh" (Ibid.36:12), and the Torah mentions it to teach us that Timna was the daughter of a chief in Se'ir, yet she preferred to be a concubine in the family of Avraham than an esteemed wife among her own people.