S. R. Faruqi:

In this verse the word 'now' is very meaningful. The suggestion is that idol-temple and Ka'bah have no fixed rank, it's all a matter of belief and imagination. Since we no longer have a mind to rub our forehead on every door, we have supposed that we ourselves are an idol-temple, we ourselves are the Ka'bah. And when we imagined this, then this very thing became the reality as well.

The point is also fine that although idol-temple and Ka'bah are opposites of each other, and cannot be brought together, nevertheless this too is only an illusion. In human existence there's both an idol-temple and the Ka'bah. Whether you consider idol-temple and Ka'bah to be symbols of falsehood and truth, or of evil and good, or illusion and reality, the fundamental thing is that both elements are present in human beings. Another point is that by 'idol-temple and Ka'bah' can also be meant the whole collection of realities. That is, that whatever is in the world, is in us; or that whatever is in the world, is us.

Then, notice too that the reason for imagining ourselves to be idol-temple and Ka'bah may be not some hidden reality or mystical self-essence, but rather only a rakish fancy-- that we don't have a mind to be kicked from door to door, so we suppose that we ourselves are an idol-temple, we ourselves are the Ka'bah. In addition, there's the fact that the search for reality (that is, idol-temple and Ka'bah) cannot be carried out through supposition/imagination; the person who searches for it only within himself is at no risk.

The final point is that those people who believe that the idol-temple and the Ka'bah are fixed and external presences are obliged to rub their foreheads on every door, because in the external world idol-temples and Ka'bahs are found in many places. Not only in the sense that in this world there are many mosques and temples, but rather because the Shaikh of every place of worship claims that the real truth and mystic knowledge are in his possession alone. Thus if you've supposed your own self to be the idol-temple and Ka'bah (or the idol-temple, or the Ka'bah), then you'll also be saved from rubbing your forehead on door after door.

As Iqbal has said in another formulation,

yih ek sijdah jise tuu giraa;N samajhtaa hai
hazaar sijdo;N se detaa hai aadmii ko nijaat

[this single prostration that you consider weighty--
through a thousand prostrations, he gives a man salvation]

FWP:

SETS == MIDPOINTS; OPPOSITES
MOTIFS == RELIGIONS
NAMES == KA'BAH
TERMS

The verse consists of two independent sentences in the first line, and an apparently impatient question in the second line. The second of the two sentences in the first line is arranged and positioned in such a way that it can easily be read either with the first sentence ('Now the truth is, after all, that we ourselves are idol-temple and Ka'bah') or with the second line ('Now the truth is, after all, who wants to go around doing prostrations at door after door?'). The former sounds like an affirmation of belief, the latter like a sly wink of cynicism.

As SRF notes, the 'now' is also important; it signals either a newly elevated mystical state ('Now we are idol-temple and Ka'bah, formerly we were not') or a newly cynical attitude ('Now we're too lazy or worn-out for door-to-door forehead-rubbing, formerly we were not'). There's also that colloquial little to that's so hard to translate-- I've gone with 'after all,' but 'well then' or 'so' or some other little sentence-rebalancer would have been as good (and just as inadequate).

There's nice wordplay of course between dimaa;G as 'head', and 'forehead'.

Note for grammar fans: It's tempting to read hamii;N as the Persian one meaning 'equal, the same'. To an English-speaker, accustomed to plural verbs for plural subjects, that looks exactly right. But in Urdu a string of subjects tends to receive a singular verb agreeing with the last item in the string. And especially since dair-o-;haram is unified by the conjunction, the pairing should really receive a singular verb (something like 'idol-temple and Ka'bah-- it's all one'). Which is a pity, because being able to read hamii;N as 'equal, the same' would also work wonderfully to enhance the possible interpretations of the verse.