What is the meaning of "Im la'Letzim Hu Yalitz"?
Rashi: If one is drawn after scoffers, in the end also he will scoff with them.
Sha'arei Teshuvah (3:175): Letzim mock people. (It is due to pride, the opposite of humility.) Hashem mocks them - "Yoshev ba'Shamayim Yischak Hashem Yil'ag Lamo" (Tehilim 2:4). "Im" shows the truth of the matter, like "Im Yihyeh Leva'er Kayin" (Bamidbar 24:22).
R. Yonah (Avos 3:2): Shlomo consoles those who are mocked, and do not answer. Hashem mocks those who mock you - they lose more via scoffing than you do!
Malbim: Hashem will cause that everyone will mock and talk about scoffers - Midah k'Neged Midah.
Why does it say "vela'Anavim Yiten Chen"?
Rashi: If he will attach himself to the humble, in the end his deeds will find grace in the eyes of people.
R. Yonah (Avos 3:2): Hashem gives grace to those who bear mockery, and do not answer.
Malbim: The humble are not haughty to argue with the laws of Chachmah. Amidst humility, they know that their Sechel is too small to understand hidden matters. Hashem will give to them grace in the eyes of people.
