Why does one who goes with Chachamim become wise?
R. Yonah: He becomes secondary to them.
Orchos Tzadikim (Sha'ar ha'Anavah DH Harbeh Anafim): A humble person merits to grow wise, for he is humble in front of Chachamim and wallows in the dust of their feet.
Orchos Tzadikim (Sha'ar ha'Chanfus DH Derech): He learns from their deeds [Malbim - and their Chachmah, and does according to the laws of Chachmah. "Holech Im" shows that he will not be their peer immediately, rather, he will go after them, for Chachmah is hard to learn.]
Ma'alos ha'Torah (DH ha'Chlal ha'Yotzei): One who clings to a Tzadik merits to be like him. Because Lot clung to Avraham, he merited to be like him - "v'Gam l'Lot ha'Holech Es Avram" (Bereishis 13:5).
What is the meaning of "v'Ro'eh Kesilim Yero'a"?
Rashi: He joins to Kesilim; they are his friends. He will be shattered.
R. Yonah: One who become the head of Kesilim - "v'Nasati Lachem Ro'im k'Libi v'Ra'u Eschem" (Yirmeyah 3:15). He will be broken. This is like "Tadik v'Sero'a" (Daniel 2:40). Chazal said, one should be the tail of lions, and not the head of foxes (Avos 4:15).
Mesilas Yesharim (Perek 5): Even after a person knows the obligation of Avodah and carefulness in it, he will slacken or transgress matters, lest his colleagues mock him, or in order to mingle with them.
Ma'alos ha'Torah (DH ha'Chlal ha'Yotzei): When Lot clung to Avraham, he was like him. When he clung to people of Sedom, he was caught with them.
Malbim: One who joins to Kesilim will be broken. He will learn from them to pursue desire. They will teach to him Iveles, and he will not know the laws of Chachmah at all. He will be their head immediately. Ro'eh is one who conducts them. Even though it seems that he conducts them, in the end he will be broken.
