1)
Which humble will inherit the land?
1.
Radak: Those who are lowly in front of the Resha'im, when the Resha'im perish, they will inherit the land.
2)
Why will they delight?
1.
Radak: When Resha'im perish, there is Shalom and Simchah in the world - "uva'Avod Resha'im Rinah" (Mishlei 11:10).
2.
Malbim: The humble have two advantages over the evildoers. (a) Their success will endure; in the end, they will inherit the land. (b) Their success is not illusory (like the Rasha's; his heart is full of worry and agitation), rather, pleasure over great Shalom.