1)
When will David's Nefesh rejoice?
1.
Rashi: When he sees their downfall.
2.
Radak: When he gets vengeance from his enemies who wanted to take his life.
2)
Why does it say "Tagil ba'Shem Tasis bi'Yshu'aso"?
1.
Malbim: Joy in his heart will be via Hashem. The exposed joy will be via His salvation. This verse discusses Simchah over salvation from their plot against his Nefesh; also refer to 35:10:3:2.
