S. R. Faruqi:

Here risālah is a military word, with regard to it pareshānī and barham have a great affinity. For the heart to 'come into the hands' is also very excellent, and also the 'implication' that the heart has been, since its first day, in the words of Ghalib, 'an enemy of repose, and a friend of wandering' [=G{42,4}, second line]. In the first line, kuchh is a good example of colloquial usage; for without it the line would have been complete, but wouldn't have had such force.

To make risālah a metaphor for the heart is probably Mir's own invention, because I haven't seen it anywhere else. One of the heart's qualities is to be pareshān , and among its similes are the tablet [lauḥ] and the page [ṣafḥah]. In this connection we can also call risālah a zila for dil , if risālah is taken in its original meaning as 'pages, book'.

It should be noted that the authors of [the Indo-Persian dictionaries] bahār-e ʿajam and ānand rāj have both given risālah meaning 'part of an army' as a Hindustani military term, and in that meaning it doesn't exist in Arabic and Persian. Just look at Mir's craftsmanship, or masterful cleverness, that risālah in its Hindustani meaning is a zila of dil , and in its Arabic meaning is also a zila of dil .

FWP:

SETS == WORDPLAY
MOTIFS == WRITING
NAMES
TERMS == AFFINITY; ZILA

SRF has analyzed the wordplay that's the chief feature of the verse, and I have nothing special to add.