"a house": Whence do I derive (the same for) a straw loft, a cattle shed, a wood hut, and a treasure store? From "who has built" (— any manner of building). I might think then that also included are gateways, porticos, and porches; it is, therefore, written "house." Just as a house can be "inhabited," so, all that can be inhabited, to exclude the above, which cannot be "inhabited."
"and did not inhabit it": to exclude a (house) robber.
"let him go and return to his house": (Let him) heed the words of the Cohein at the battle formation and return,