R. Yonah #1: See the difference between Leshon Chachamim and Kesilim's mouth! It is not enough that Chachamim teach the way of Da'as, and say 'go in this way.' Their tongues beauty Da'as and add reason and metaphors, until the hearers accept the Da'as, and it is pleasant to them. Teitiv is to beautify. "Tovas Mar'eh" (Bereishis 26:7) is accepted and a beautiful appearance; "va'Teitev Es Roshah" (Melachim II, 9:30), "b'Heitivo Es ha'Neros" (Shemos 30:7) it is an expression of fixing.

R. Yonah #2: Leshon Chachamim improves the Da'as of people ¹ .

Malbim: Da'as applies to sensed matters, or what is known clearly as if it was sensed. Chachmah is received. There are no proofs for it, and the senses do not perceive it. Even so, Leshon Chachamim Teitiv Da'as. Leshon refers to speech of Tevunah. If they speak this way in Chachmah, it will be clarified to them to the level of Da'as. "Chachamim Yitzpenu Da'as" (10:14) - they do not reveal it to everyone, only to Nevonim. Leshon refers to speech hidden in Binah. However, when they speak externally, with the lips, they make a gold crown around and conceal their words - "Sifsei Chachamim Yezaru Da'as" (7).

Malbim: Even though the Kesil received the laws of Chachmah, desire overpowers him. Therefore, he puts doubts in the laws of Chachmah; this is called Iveles. He does not speak with the tongue or lips - speech of Tevunah and Da'as - for a Kesil does not understand this. His mouth speaks only Iveles and doubts. The mouth hints to speech of Chachmah. The Kesil speaks Iveles, the opposite of Chachmah. The source of Iveles is in his mouth, and not in his heart - "v'Iveles Kesilim Mirmah", "Iveles Kesilim Iveles" (14:8, 24). His heart is not unsure; Iveles comes from his mouth.