1)
What are "Chasadecha ha'Rishonim"?
1.
Radak: It is what You swore to David in Your Emunah. Where is it? You abandoned us in Galus!
2.
Malbim: This is the Chesed (choosing David, not due to merit).
2)
Why did Hashem swear?
1.
Malbim: This was corresponding to Emunah (due to his merit). It was for the sake of the path of perfection of the Klal - "va'Tedaber Gam El Beis Avdecha leme'Rachok v'Zos Toras ha'Adam Hashem" (Shmuel II, 7:19).
