taskiin : 'Calming, stilling, tranquillizing, appeasing, soothing, allaying, assuaging; consolation, comfort, mitigation, rest, assurance, peace (of mind)'. (Platts p.324)
aasaa))ish : 'Ease, rest, repose, quiet, tranquillity; convenience, comfort; indulgence, enjoyment'. (Platts p.47)
be-taabii : 'Faintness; agitation, restlessness, uneasiness, impatience; lack of splendour or lustre'. (Platts p.204)
The Moth is the symbol/representative of faithfulness; and the candle-flame, of cruelty/oppression. If the faithfulness-practicing lover would remain in peace/comfort, then the cruel, oppressive beloved remains agitated. The candle-flame is restless. Perhaps if the Moth would come into it and burn, then the flame would find peace, because the ease/rest of the faithful one would be going away.
For more on Ghalib's unpublished verses, see the discussion in {4,8x}. See also the overview index.
The verse is straightforward; Zamin and Gyan Chand explain it well.
It's common in the ghazal world to contrast vafaa and jafaa ; their opposite meanings are made more intriguing by their extreme similarity of spelling and pronunciation. But the present verse unfortunately breaks the symmetry by pluralizing vafaa into the awkward vafaahaa , which sounds a bit silly (and even like the beginning of a laugh), while contributing absolutely nothing to the meaning of the verse. (Ghalib was fond of such pluralized abstractions; for more examples, see {1,2}.)
The only possible reason to pluralize it would be for padding, to fill in that extra syllable required by the meter. The location of the haa syllable right before the caesura has the further unfortunate effect of giving it extra emphasis.
Zamin:
The flame of the candle is agitated (trembles). He says that until the Moth would fall into its flame and burn up, it's impossible for the candle to be at peace. Because from the rest/repose of faithfulness (the people of faithfulness), cruelty/oppression (the people of cruelty/oppression) remains agitated.
== Zamin, p. 407