Shabbos 88b: After every utterance of Hashem, Yisrael's souls left them - "Nafshi Yatz'ah v'Dabro" (Shir ha'Shirim 5:6). Hashem revived them with dew that will be used for the ultimate Techiyas ha'Mesim.

Rashi: You did also this for us - if we needed rain, You always waved and cast on us rain of Nedavah and Brachah.

Radak: "Shamayim dripped" (verse 9) hints to afflictions that You 'drip' on the enemies. For Yisrael it is the opposite - You wave rain of Nedavah for them.

Malbim: When David's camp camped in the Midbar, they were weary from thirst. Rain descended; it was like cold water on a weary Nefesh. It is as if Hashem is obliged to send rain in settled places for His creations, but in the Midbar he is not obligated; it is Nedavah and Chesed.

Refer to 68:10:1:1.

Rashi: When the inheritance of Your land was weary and thirsty for rain, You prepared it.

Radak: Yisrael is Your Nachalah - "v'Hem Amecha v'Nachalasecha" (Devarim 9:29). "V'Nil'ah" is like v'Im ¹ Nil'ah (if it became weary). I.e. if Your inheritance became weary in the enemy's hand - it already seized all Arei Yehudah - You prepare it lest it be totally abandoned. You do not give Yerushalayim in the enemy's hand.

Malbim: You prepared (sustained) the tired and weary from heat and thirst.