Chagigah 15b: This was R. Meir's source to learn from Acher (even though he went off the Derech). It does not say v'Libecha Tashis l'Daitam (for they are Resha'im), rather, "l'Daiti". Rashi - learn from any Chacham, but if he is a Rasha, do not learn from his deeds.

R. Yonah: Put your heart to understand My primary intent in everything, and which path I intend to make you reach. The matters are deep; you will reach their intent only if you put to your heart to contemplate them.

Malbim: Chachamim's words of Chachmah are a tradition. They received the laws of Chachmah from Hashem; there is no proof for them. One must receive them from mouth to ear. However, Shlomo said "Lada'as Chachmah u'Musar" (1:2); via his Meshalim, he explained the laws of Chachmah so a person can reach Yedi'ah (clear knowledge) of them. You must tilt your ear to hear Divrei Chachamim via tradition. After you receive them from tradition, they will be fixed in your heart via trusting in Hashem who gave them; He knows their Emes. Then you will put your heart to my Da'as, according to how I explained its laws. If you will not accept them first, my Da'as will not help you, for you will contradict their foundations.