What water should you drink from your pit?
Rashi: The pit that Hashem gave for your portion - Toras Moshe. Bor is gathered water.
Malbim: As opposed to the Yetzer's enticement to dig "broken pits that do not hold water" (Yirmeyah 2:13), drink water from your pit - Chachmah and Da'as.
What are "Nozelim mi'Toch Be'erecha"?
Rashi: It is flowing water. First [Divrei Torah] are like gathered water, and at the end they flow and increase.
Malbim: A Bor is gathered rainwater. A Be'er is flowing water. The beginning of learning Chachmah is compared to gathered water. One receives the laws of Chachmah only via tradition. Afterwards, they flow in your Be'er. Afterwards they were like a well and overpowering spring. He finds new Chidushim from his Da'as; they flow outside to teach Chachmah to others 1 .
Ma'alos ha'Torah (DH R. Shimon): Just like a well makes water flow on all its sides, so a Talmid Chacham.