How does he dig evil?
Rashi: He plots evil in his heart.
R. Yonah: He 'digs' and delves deeply in his thought. Above (23), it said that a Chacham thinks about a matter of Chachmah before he speaks, and thinks more while saying it. Here it teaches that also the Rasha delves deeply in thought of evil, and adds to it when he tells his friend amidst heat of desire [to fulfill it, "k'Esh Tzareves" - PF].
Malbim: After teaching that the way of Chachmah clothes one with humility, Bitachon and Ru'ach ha'Kodesh, and enables him to return others to the [proper] path, it discusses the way of a Kesil, which is opposite. Ish Beliya'al totally cast off the yoke of Shamayim. He digs a deep pit to make his colleague fall.
What is "k'Esh Tzareves" on his lips?
Rashi: The evil is like burning fire on the lips, until he says it. Tzareves is burning, like "v'Nitzrevu Vah Kol Panim" (Yechezkel 21:3).
R. Yonah: Tzareves is the evil. It is hot like fire; it is an adjective. "V'Tzareves ha'Shechin" (Vayikra 13:23) is a noun.
Malbim: It is excitement, with flames of love, to the point that Tzareves ha'Michvah (burned skin) appears on the lips - "Kesef Sigim Metzupeh Al Charesh Sefasayim Dolekes v'Lev Ra" (26:23). His lips speak love, but internally he sets his ambush 1 .
Yirmeyah 9:7 says like this. (PF)
