1)
What is the meaning of "b'Fesha Ish Ra Mokesh"?
1.
Rashi: A trap will come [via an evil man's sin].
2.
Malbim: Sin itself is the trap in which the evil man is caught.
2)
Why does the Tzadik rejoice?
1.
Rashi: He did not go in the Rasha's ways.
2.
Malbim: Then Hashem's Mishpatim are seen - "Tav'u Goyim b'Shachas Asu