FWP:
SETS == A,B; GENERATORS; JO
Walls and doors are at once barriers (when we look at them we can't see any further) and points of access (the breeze and the Messenger would come through the door, the breeze perhaps through crevices in walls as well). When we look at walls and doors, we want instead to look through and beyond them. This is complex in itself, but more layers of possibility are built into the very grammar of seeing. The difference we make in English between 'look at' and 'see' can't be expressed in Urdu (any more than can 'listen' and 'hear'). So dekhnaa can be taken either way. And there's also the sense of 'see' to convey 'see as' ('when I look at you, I see Doomsday').
So in short, it's far from clear-- as far from clear as Ghalib can possibly make it, in fact-- what is being looked at, and what is being seen, and what is being seen as what. Essentially, the lover 'sees' A and B, 'sees' sometimes C, sometimes D. Here are some of the possibilities:
=The lover looks at a door and sees it as the entry point for a Messenger.
=The lover looks at a door and sees it as a Messenger (since he's desperate and half-mad).
=The lover looks at walls and sees them as the entry point for the breeze.
=The lover looks at walls and sees them, because of their crevice-work, as the breeze
itself (since he's desperate and half-mad).
=The lover looks at the breeze, and sees it as a Messenger.
=The lover looks at the Messenger, and sees him as the breeze (which is also a messenger).
=The lover looks at the breeze, and sees it in visible form as a wall (with crevice-work
through which messages can come).
=The lover looks at the Messenger, and sees him as a door (providing access to the
beloved).
And so on, into increasingly bizarre possibilities. Of course this is a somewhat insane degree of mutability, but then, the lover 'in separation' [hijr me;N] is more than a little insane himself. And it's a clever touch for the verse to provide both a 'normal' meaning (such as the commentators explain), and a wild breakdown of meaning into hallucinatory confusion (such as the grammar of the verse undeniably facilitates).
On the flexibility of jo , see {12,2}.
On the nature of crevice-work in walls, see {64,4}.
For the ultimate 'doors and walls' ghazal, see {58}.
Nazm:
The breeze comes and goes everywhere, and has access everywhere without hindrance. For this reason, among poets the messenger-ship of the breeze is famous; there's no better Messenger than the breeze. The meaning is that we are waiting: when will the Messenger appear in the doorway, and when will the breeze blow in? (110)
== Nazm page 110