Why are Tzadikim compared to date and cedar trees?
Rashi (based on Bava Basra 80b): They yield fruits like date trees, and regenerate like cedars. Malbim - after a date tree sprouts and makes fruits, it dries, and if it is cut, it does not regenerate. A cedar always grows; if the stump is cut, it regenerates. Tzadikim have both attributes. They have Kadosh fruits (children), and persist like cedars (their spiritual Nefesh lives forever).
Radak: They are taller than all other trees.
Radak citing Shocher Tov: A date tree's shade is far from it (it is tall and thin) - so Tzadikim, their reward is far from them; it is not until the world to come. People do not make Kelim, tables and candelabras from date trees. Do not say that Yisrael are similar - therefore it mentions cedar.
Malbim: Everyone who sees, recognizes and says that via evildoers rising against a Tzadik, he sprouts like a date tree, is elevated and succeeds.
Why does it mention a cedar "in Levanon"?
Radak: It discusses a common case; Levanon was a forest in Eretz Yisrael.
What is the meaning of "Yisgeh"?
Radak: [It will grow and sprout] greatly. This is like "Sagi Cho'ach" (Iyov 37:23, i.e. great strength). The Targum of "Rav" (Devarim 3:19) is Sagi.
