S. R. Faruqi:

When there would be a commonplace type of meeting with someone, without any connection of friendship, then people say, 'so-and-so is our acquaintance', or 'we are so-and-so's acquaintance'. In a mirror appears the reflection of every person who comes before it, but the reflection doesn't remain in the mirror-- thus the speaker has said that the mirror is only an 'acquaintance'. The affinity of 'heart' and 'mirror' is clear.

But the point is that in the heart there was a kind of agitation, there was a restlessness, or perhaps there was fickleness [harjaa))iipan]. The result was that we didn't settle in any one place, or become captivated by the love of any one person. Because of wandering from door to door, many people became our 'acquaintances'. But no one became a friend. If in us was a mirror-like clearness, then there was a mirror-like fickleness as well.

Another reading is that our heart was like a mirror, in which the whole world was being reflected. Or perhaps 'a single world' refers to our own existence, which is convoluted and deep and many-colored like the whole world. In the mirror of the heart we saw ourselves, as if we saw a whole world. Or else we saw that we ourselves are a single world, or that we maintain our own private world. The heart is a mirror; if it would be polished, then the world and the events of the world become reflected. This is a special topic of the Sufis.

Thus Maulana-e Rum has said [in Persian], in his Masnavi (daftar 1, part 2):

'This clearness of the mirror is a quality of the heart.
Such a heart is fit to reflect limitless aspects.'

Qa'im has also versified this theme. But he replaced 'heart' with the word 'amazement', and made the meaning explicit and limited:

;hairat ne kiyaa hai ek jahaa;N kaa
juu;N aa))inah ruu-shinaas mujh ko

[amazement has made of a world
like a mirror, an acquaintance to me]

FWP:

SETS == EK; FILL-IN; MIDPOINTS
MOTIFS == MIRROR
NAMES
TERMS == AFFINITY

The first line has a conspicuous 'midpoint' construction: the adverbial mi;saal-e aa))iinah can refer either to the speaker's action (the speaker became, or behaved, like a mirror), or to the heart's action (the heart became, or behaved, like a mirror). (It's already clear that these 'midpoints' are a very Mirian structural feature.) And mi.saal can also be used to mean either a weaker 'like' of some unspecified kind (X is like Y), or a stronger, more emphatic 'in the likeness of' (X took on an appearance that particuarly resembled that of Y).

SRF observes that 'heart' and 'mirror' have a strong affinity; this is through centuries of Persian ghazal practice in which the heart 'mirrors' God, etc., and in which the heart-mirror can be clean, dirty, polished, unpolished, etc. in a steady flow of fresh themes. So in rhe present verse, either the heart made us into something mirror-like, or the heart, mirror-like, made us into something. In either case what it made us into was an 'acquaintance'-- literally, someone 'face-knowing' [ruu-shinaas]; this is spectacularly suitable wordplay, since what else can be a mirror's stock in trade except the 'face' of things, and other visible surfaces? By its very nature, a mirror seems to offer a 'superficial' (literally, 'surfacey') view.

And a view of what? Of an ((aalam (see the definition above), which can be anything from a 'world', through an 'era', to a (frequently Sufistic) 'state' or a 'beautiful sight'. The only adjective provided for this condition is the almost morbidly wide-ranging ek . So is the speaker lamenting the limitations of his merely superficial view, or rejoicing in its extensiveness and fascination? Is he seeing (something of) the outer world, or finding a world in his own heart? Does he consider being a 'face-knower' a desirable thing, or a cause for despair? The tone too is crucial-- and of course, it too is left to us to supply.

In short, the verse is an intriguing example of what I call a 'fill-in' verse-- we ourselves have to decide on the nature of the 'world', its moral valence, and the kind of spectacle it offers. Perhaps our choices will depend on how we ourselves think about mirrors.