What happened from when Hashem commanded Shoftim over them?
'Rashi': They did not have serenity like you - I subdued all your enemies in front of you.
Vilna Gaon, Rashi (Shmuel II, 7:11): This refers to the end of the previous verse - [Resha'im will no longer afflict them like they did initially,] and from when Hashem commanded Shoftim [until now].
Radak: Initially, [Bnei Avlah] were Mechaleh (destroyed) Yisrael. From when Hashem commanded Shoftim, they still afflicted them. Even though the Shoftim saved them, there was not full serenity until now.
When will he have this serenity?
Malbim (Shmuel II, 7:11): It will be at the end of David's life, when Hashem will fix a place for absolute rest - Aravna's granary, where Shlomo will build the Mikdash. Once the place is fixed, the wars will cease, and then David began preparing all needs of the Mikdash (below, Perek 22).
When will Hashem tell him about building the Bayis?
'Rashi', Rashi (Shmuel II, 7:11): Today, through me (Nasan).
Malbim: It will be later - after David killed many in war, Hashem told him that this is the reason why he cannot build the Beis ha'Mikdash, like it says below (28:3).
What house does this discuss?
Targum Yonasan (Shmuel II, 7:11): It is a house of kingship. 'Rashi' - you wanted to build His house, so He will build your house. He will seat your son on your throne, and he will build the Beis ha'Mikdash.
Vilna Gaon 1 : Really, Hashem will build the Beis ha'Mikdash, just because David's heart totally wanted to build it, it is attributed to him - "Chanukas ha'Bayis l'David" (Tehilim 30:1). Also the builders did not do anything. The Bayis built itself; the rocks ascended on the rows (Bamidbar Rabah 84:3). And so said Shlomo "Im Hashem Lo Yivneh Bayis (the builders toiled for naught)" (Tehilim 127:1).
