How are "Divrei Fi Chacham Chen"?
Rav Sadya Gaon: A Chacham's words pour grace on him.
Rashi: People hear and heed him. He receives grandeur for [his words].
Ibn Ezra: Heaven forbid that a Chacham would be a Ba'al Lashon! All the words that leave his mouth are grace.
Rashbam: A Chacham speaks gently, with appeasement and properly. This gives to him grace in the eyes of people.
Ri Kara: His words are reward for him.
How do a Kesil's lips swallow him?
Rav Sadya Gaon: The speech of a Kesil's lips makes him perish.
Rashi: This is one who entices his friend from the good path. E.g. Bil'am breached the nations' fence from Arayos from the flood and onwards, and counseled them to make their daughters Hefker for Zenus.
Rashbam: Each of his lips 1 speaks with pride. This swallows him from the world, for he is disgraced and despised in the eyes of people.
I do not understand this. Letters that require the lips (Beis, Mem, Pei), one lip cannot say them by itself! He came to answer why Teval'enu" is singular, even though "Sifsos" is plural. Ibn Ezra - we find like this, e.g. "Zevuvei Maves Yavish" (1).