Who is the Tzadik?
Rashi: It is Yisrael.
Radak: They are virtuous and good people.
Malbim: He is what will sprout from the cut grass and rain (rebuke). He will do acts of Tzedek and conduct according to it.
Why does it say "v'Rov Shalom"?
Rashi: Great Shalom will sprout in his days; it will last forever. This entire Tefilah was fulfilled, except for this, for Shlomo sinned, therefore his kingship did not last. Kingship was given to David on condition that his children guard Hashem's ways. Yisrael sprouted in his days - "Yehudah v'Yisrael Rabim k'Chol Asher Al ha'Yam" (Melachim I, 4:20). There was great Shalom - "va'Yeshev Yehudah v'Yisrael la'Vetach Ish Tachas Gafno v'Sachas Te'enaso... Kol Yemei Shlomo" (ibid., 5:5).
What is the meaning of "Ad Bli Yare'ach"?
Radak: [Until the moon ceases to exist,] i.e. as long as the world exists. If it refers to Shlomo, it is an exaggeration. If it refers to Mashi'ach, the simple meaning is true - there will always be Shalom.
Malbim: Forever.
