Why did He say "Ki Mal'u Yamecha"?
'Rashi': Do not fear lest I hasten the matter. After your days are completed, I will establish your seed after you.
Radak (Shmuel II, 7:12) #1: This is not a Brachah. Rather, when your days will be completed, and you will die...
Radak (Shmuel II, 7:12) #2: This is a Brachah. He will die old, after a full long lifetime, which is 70 years, like it says "Yemei Shenoseinu Shiv'im Shanah" (Tehilim 90:10). David became king at the age of 30, and was king for 40 years. And so we explain "I will fulfill the number of your days" (refer to Shmuel 1 26:5:1:1*).
Radak (Shmuel II, 7:12, citing Yerushalmi Brachos 2:1): I will count full days for you, and not lacking days. 1
Bamidbar Rabah 14:12: Hashem told David that he will live all the years allotted for him. Adam was supposed to live 1000 years. He gave 70 of them to David. Yefe To'ar (Bereishis 58:1) ? he will finish his last year (die on his birthday, like it says about Moshe "Me'ah v'Esrim Shanah Anochi ha'Yom" (Devarim 31:2. According to Shabbos 30b, David did not know this. Hashem told him only that he will die on Shabbos, and every Shabbos, David would learn Torah the entire day so the Satan could not take him. ? PF)
Why did He say "to go with your fathers"?
Malbim: Ezra revealed that Tzadikim do not rest in this world, and not in the world to come - "Yelchu mi'Chayil El Chayil" (Tehilim 84:8; Brachos 64a), "v'Nasati Lecha Mehalchim Bein ha'Omdim ha'Eleh" (Zecharyah 7:3).
Why did He say "I will establish your seed after you"?
Malbim (Shmuel II, 7:12): He will not rule over you in your lifetime, like Avshalom attempted. 1
Even though Shlomo was anointed in David's lifetime, and he reigned in David's life (this is almost explicit in Melachim I, 1:39-53, and so wrote Malbim there, verse 35), he did not rule over David, rather, with his permission. (PF)
Why does it say here "Asher Yihyeh mi'Banecha"? It says in Shmuel II, 7:12 "Asher Yetzei mi'Me'echa"!
Malbim: Ezra revealed that it will be from David's sons, and not from the seed of David's daughters.
Radak (Shmuel II, 7:12) learned from the verse that it will be someone not born yet, and not Avshalom or Adoniyahu (like it says below (22:9) "Hinei Ven Nolad Lecha... 1 ." Perhaps also our verse teaches this. (PF)
Radak: David did not yet know who it will be, until Nasan called Shlomo "Yedidyah" (Shmuel II, 12:25). Or, Nasan explicitly told David. Even though it is not recorded in his words here in Sefer Shmuel or here, we find that David told Shlomo (below 22:8-10) "Alai Devar Hashem?.; [Ven Nolad Lecha?] Shlomo Yihyeh Shmo?; [Hu Yivneh Bayis Lishmi]" (The verses imply that before Shlomo was born, David knew that Shlomo will build the Beis ha'Mikdash! This is difficult for Radak's first Perush, that he knew only after Nasan called him "Yedidyah! - PF)
Why does it say here "v'Hachinosi Es Malchuso"? In Shmuel II, 7:12 it says "v'Hachinosi Es Mamlachto"!
Malbim: Mamlachah refers to kingship over the entire nation. This was not fulfilled [after Shlomo], for the kingship was split in two. David's seed retained Malchus over Yehudah.
