1)
Where did Hashem promise serenity to Yisrael?
1.
Rashi: "V'Heni'ach Lachem mi'Kol Oyveichem" (Devarim 12:10).
2)
Why did he mention Hashem's promise of serenity?
1.
Malbim: It was possible to build the Beis ha'Mikdash only after they had serenity, like I explained (Shmuel II, 7:13). After the promise of serenity, Hashem promised to choose a place for His Shechinah (Devarim 12:10-11) - "v'Nasati Mishkani b'Sochechem" (Vayikra 26:11).
