R. Yonah: After saying that one whose heart is sad, words are a burden to him, e.g. a stingy person when he feeds others. Here it warns similarly not to say Divrei Chachmah to a Kesil. He will not love them; he will disgrace them. For the honor of Chachmah, one should speak its words only to one who will love and cherish them. 'Do not be like one who casts pearls to pigs.'

Malbim: Evvil is unsure about the laws of Chachmah. A Kesil, sometimes he knows the laws of Chachmah, but he is estranged from them due to his desire. An Evvil, if one can prove to him the laws of Chachmah, he would retract from his folly. A Kesil flees from Chachmah, even if he knows its value, for it muzzles his desire. One cannot give proofs of Tevunah for the laws of Chachmah, but Sechel has a sharp power to make them understood. A Maskil can speak in an Evvil's ears; perhaps he can return him from his folly. This is not so for a Kesil, like I explained "Lech mi'Neged l'Ish Kesil u'Val Yadata Sifsei Da'as" (refer to 14:7:1:3).