1)
Why should he stay in his house?
1.
Rashi: This was to show [Bnei ha'Golah] that they are not worthy of rebuke.
2.
Radak: First He commanded him to be silent among them, to inform that his silence is like his speech, for they are Beis Meri (they will not accept rebuke). Afterwards He commanded him to stay in his house, and not go among them, lest he rebuke them before Hashem finished all his Nevu'os, until "v'Ru'ach Nesa'asni va'Tevi'eni Chasdimah" (11:24).
3.
Malbim: Before he began to prophesize, he needed to be shut up all the days of the siege below (4:5-6), in order to bear the sin of Yehudah and Yisrael via lying on his side.
