What do we learn from "Lo Ye'uneh la'Tzadik Kol Aven"?
Rashi: A Tzadik will not stumble in a sin unknowingly 1 .
Yevamos 121a, Nidah 65a: A Tzadik will not stumble via giving a mistake ruling.
R. Yonah: Hashem guards a Tzadik from mistakes, and helps him to overpower his Yetzer - a man guards himself from sin twice, from then and onwards Hashem guards him - "Raglei Chasidav Yishmor" (Shmuel I, 2:9).
Malbim: Anah (from the root Ye'uneh) is preparing a cause for the result, like "veha'Elokim Inah l'Yado" (Shemos 21:13; Hashem caused someone to be killed b'Shogeg). One who sinned, this is a cause of doing another Aveirah. Chazal said, if one killed (b'Shogeg, without witnesses), Hashem causes him to kill again [b'Shogeg, in front of witnesses] so he will be exiled. A Tzadik goes in the ways of Tzedek; there is no cause for him to do a sin or deed against Mishpat. No sin will occur to him, even b'Shogeg. Just the contrary, a Mitzvah leads to a Mitzvah (Avos 4:2).
Avodah Zarah 39a says so.
It says "Lo Ye'uneh la'Tzadik Kol Aven" and "Hashem Lo Ya'azvenu v'Yado"! Why does it say "b'Vala Rasha Tzadik Mimenu" (a Rasha can swallow (destroy) a Tzadik)?!
Brachos 7b #1: A Rasha can destroy someone more righteous than himself; he cannot destroy a perfect Tzadik.
Brachos 7b #2: A prospering Rasha can destroy a Tzadik.
How are Resha'im full of evil?
R. Yonah: They are full of countless sins - an Aveirah leads to another Aveirah (Avos 4:2). Once one sins and repeats it, it becomes like Heter in his eyes (Yuma 86b).
Malbim: An Aveirah leads to another Aveirah (Avos 4:2), until they are full of sin and their measure is full [to be punished for them].
