S. R. Faruqi:

There are two interpretations of the second line: (1) if Mir would compose in this ground a single perfectly-fitted line; (2) oh Mir, whoever would compose in this 'ground' a single trimly-fitted line. With regard to its affinity with misra((-e bar-jastah , the theme of throwing the cap in the air is fine, because the real meaning [in Persian] of bar-jastan is 'to leap, to bound'. Thus the line or verse of which the construction is very superior is called bar-jastah . This term is very old; thus Ibn Nishati has a verse:

la:taafat me;N hai juu;N ;xuubaa;N kii abruu
har ik mi.sra(( jo bar-jastah hai meraa

[in refinement it is like the eyebrow of beautiful ones
every single line of mine that is perfectly-fitted]

There's no doubt that to write such superb verses in a bland ground is extraordinarily enviable. The whole ghazal has seven verses. With difficulty, I rejected two verses. It seems that among Mir's contemporaries or elders no one did much with this ground.

Indeed, Baqa Akbarabadi, who considered himself superior to Mir, composed a ghazal with these rhymes, but it has only three verses. And he adopted a kind of meter that showed off these rhymes to advantage. Here is Baqa's verse with the term bar-jastah :

az-bas huu;N baqaa shaa))iq us ma:tla((-e abruu kaa
aah-e sa;hrii merii hai ma:tla((-e bar-jastah

[to such an extent, Baqa, I am devoted to the 'opening-verse' of her eyebrows
my sigh of the dawn is a perfectly-fitted verse]

Shah Hatim adopted the meter of Mir's ghazal (his ghazal is from 1753-54, so it's possible that it might be after Mir's ghazal, or from the same period), but he adopted the ground sar-bastah , kamar-bastah ; thus his opening-verse is:

chalaa hai kis :taraf tuu aaj shamshiir-o-sipir-bastah
mai;N sar dene ko bai;Thaa huu;N yahaa;N qaatil kamar-bastah

[in what direction have you set off today, with your sword and shield bound on?
I am here, ready to give my head, oh murderer, fully resolved]

It's clear that whether with regard to harmony or to theme, Mir's verses are much better than both of these. But Hatim's rhymes have been well versified.

FWP:

SETS == POETRY
MOTIFS
NAMES
TERMS == GROUND

My theory is that bar-jastah , literally 'leaped' or 'having leaped', may describe the brilliant positioning of a word by suggesting that the word has 'leaped' into place all at once, spontaneously and powerfully. Come to think of it, this image then makes a suggestive contrast with bi;Thaanaa , to arrange or 'seat' words in a metrical line, which results in words that have been well or poorly 'seated'. Suddenly 'leaping' into position, rather than being carefully ushered in and 'seated' by the poet, does conjure up just the kind of difference (in degree, and perhaps even in kind) that is being invoked. In the first line, ba-jaa literally means 'in place', so that can count as an additional touch of wordplay.

Of the two readings proposed by SRF for the second line, the latter reading seems much the better one. Partly because Mir has just finished composing no fewer than eight verses with this refrain, so it would be strange if he spoke of his pride at composing even one such line in hypothetical terms (with the future subjunctive). And partly because a boastful use of the closing-verse is so common in the classical ghazal.