The Italian word 'stanza' means 'a room', and a room is a good way to conceive of a stanza. A room, generally speaking, is sufficient for its own purposes, but it does not constitute a house. A stanza has the same sense of containment, without being complete or independent.
The iambic pentameter owes its pre-eminence in English poetry to its genius for variation. Good blank verse does not sound like a series of identically measured lines. It sounds like a series of subtle variations on the same theme.