Why does it say "b'Feh Chanef Yashchis Re'ehu"?
Rashi: He entices his colleague to an evil path - he destroys him with his mouth.
R. Yonah: This discusses flattery. He destroys him with his mouth, for he praises him for an attribute that he does not have. He causes him to be "To'avas Hashem Kol Gevah Lev" (16:5).
Orchos Tzadikim (Sha'ar ha'Chanifus DH ha'Shelishi): Even if he does not praise him in public and cause Rabim to stumble, he makes the Rasha stumble in pride, and he will not repent.
Malbim: One who flatters and does not rebuke, he wants to destroy his friend - "Gever Machalik Al Re'ehu Reshes Pores Al Pe'amav" (29:5).
How is the Tzadik saved via Da'as?
Rashi: Da'as of the Torah warned him [not to accede] - "Lo Soveh Lo" (Devarim 13:9).
R. Yonah #1: Tzadikim are saved from flattery via their Da'as. Their Nefesh does not stray to be haughty due to praise of people. 'You must be a Tzadik, and not a Rasha. Even if everyone tells you that you are a Tzadik, consider yourself a Rasha' (Nidah 30b).
R. Yonah #2: Tzadikim's Da'as saves others - they rebuke them, the opposite of the flatterer's Midah.
