S. R. Faruqi:

The style of implication has has created such eloquence [balaa;Gat] in this verse that force of expression sacrifices itself for it. The wounds in the breast are marks of passion. These scars are either from those wounds that the beloved has created, or from the stones that boys have thrown, or from those bloody tears that have dripped from the eyes.

It's clear that the idea of washing them is inappropriate-- that is, it doesn't happen that someone would receive wounds in the breast, and then would sit down to wash them away. Thus in the second line, by the washing of the wounds is really meant the shedding of tears.

In the verse is an ironic tension. Tears are continually falling on the breast, and the speaker has interpreted the shedding of tears (which is a sign of grief) as an attempt to wash away the scars/wounds. That is, he considers it to be an attempt to wash away grief. It's extraordinarily melancholy that the action that is a symbol of extreme grief would be interpreted as an attempt to find release from grief.

This verse and the previous verse [{71,3}] seem to be influenced by this [Persian] verse of Zuhuri's:

'I sowed in my breast nothing but wounds,
the clouds of my eyes acts as spark-scatterers.'

But in Zuhuri's verse there's not the dramaticness and ironic tension that's in Mir's verse. The ambiguity of the addressee in Mir's verse is also fine. If the speaker isn't addressing himself, then the addressee is some inexperienced lover and the speaker is some worldly-wise person, or perhaps a physician (or the beloved herself).

FWP:

SETS == EXCLAMATION
MOTIFS
NAMES
TERMS == IMPLICATION

Here daa;G seems to mean 'scar' rather than 'wound'. Its ability to mean either or both (see the definition above) is just one more form of convenient ambiguity that the poets can use to torment (and entice, and entertain) us. The sarcastic reference in the first line to washing the marks away is what establishes the sense of 'scar': that would be a possible thing to think (wistfully?) of doing to an old scar, but not a plausible reaction to a fresh, bloody, open wound. But in any case, as SRF explains, the implication of tears removes any sense of real volition.

Note for grammar fans: It's true that we could read the first line as a single utterance, with jaate nahii;N hai;N presented (archaically) out of order: 'These marks of passion do not go away'. It would be unusual to provide the hai;N with the negative, but it could be seen as emphatic. But isn't that a less colloquial, less vivid way to read the line? That note of impatience (or even exasperation) would be lost, and it's hard to think of anything that would be gained.