From what affliction should Hashem answer you?
Radak: When you are at war with the enemy, He should answer your Tefilah.
Malbim: David was in a war far from Yerushalayim.
Why does it say "Yesagevcha"?
Radak: Hashem's help is like a strong tower in which one is protected; the enemy cannot rule over him.
Why does it say "Shem Elokei Yakov"?
Rashi: Hashem promised [to return] him when he went to Charan, and He fulfilled His promise.
Radak (from Devarim Rabah 2:11): Yakov was in more difficulties than Avraham and Yitzchak. A parable is a woman having a difficult birth. They said, we do not know what to tell you - but the One who answered your mother in her birth-pangs, He will answer you in yours! So it is written about Yakov - "la'Kel ha'Oneh Osi b'Yom Tzarasi" (Bereishis 35:3). Therefore, David told Yisrael - the One who answered Yakov, He will answer you.
Radak (from Brachos 64a): This teaches that [when people carry a beam together,] the owner should hold the beam in the middle (to bear the brunt of its weight). Only Yakov is [exclusively] our father. Avraham had another son Yishmael, and Yitzchak had Esav.
Radak: All of Yisrael are called [also] Yakov - "Al Tira Avdi Yakov" (Yirmeyah 30:10) and many places.
Malbim: Even though now [David] is far from the Kadosh land, Elokei Yakov should protect him there. Hashem promised Yakov when he was in Chutz la'Aretz "I will be with you and I will guard you, and I will return you to this land" - that Shem should be also for you a protection, that you will return to Eretz Yisrael.
