Who are "the humble"?
Radak: Those who repent to Hashem at the time of the Ge'ulah. Only they will see the salvation. The others will perish - "v'Heiveisi Es ha'Shelishis ba'Esh" (Zecharyah 13:9), "She'eris Yisrael Lo Ya'asu Avlah v'Lo Yedabru Chazav" (Tzefanyah 3:13).
Malbim: Those who accept with love all the affliction that befall them.
Why will they rejoice?
Radak: They will rejoice over the salvation.
Malbim: They will know that there is hope.
Who are "Dorshei Elokim"?
Radak: They are the humble. The matter is repeated in different words. They will see, and their hearts will live. It says "Levavchem" (second person), even though the verse begins in the first person. This is common, e.g. "Ki Yevoshu me'Eilim Asher Chamadtem v'Sachperu meha'Ganos Asher Bechartem" (Yeshayah 1:29).
Malbim: They investigate Elokus. Until now their heart was sad due to seeing the serenity of Resha'im and afflictions of Tzadikim. Now, their hearts will live.
What does it mean "your hearts will live"?
Radak: They will rejoice, like the verse mentioned earlier. One who worries and his heart is pained, it is as if he died - "v'Libi Chalal b'Kirbi" (109:22); the same applies to Yisrael in Galus. When the Simchah comes, the heart will live, like it says about Yakov "va'Techi Ru'ach Yakov Avihem" (Bereishis 45:27).
