What happened from when Hashem commanded Shoftim over them?
Rashi: 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].
When will he have this serenity?
Malbim: 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 (Divrei ha'Yamim I, Perek 22).
When did Hashem tell him about building the Bayis?
Rashi: Today, through me (Nasan).
Malbim: It will 1 be another time.
Our texts of Malbim say 'Higid', which implies past tense, but this cannot be, for then David would have known already that he will not build the Beis ha'Mikdash! (PF)
What house does this discuss?
Rashi, Targum Yonasan: It is a house of kingship. Malbim - Hashem will build your house, because you wanted to build His!
