S. R. Faruqi:

In the first line there's nothing special. The theme itself of the beloved's bathing in open water is such that in it no great subtlety is possible. Then, this theme will also seem displeasing to the taste of the present age. But there's no denying that before Ghalib, in all the Dihlavi poets this theme is to be found, no matter how feebly it might be versified.

For example, Jur'at composed a 'double ghazal' in this ground, and the second opening-verse of the first ghazal is as follows:

jā ke jab paire hai vuh rashk-e qamar pānī meñ
chahrah ātā hai parī kā sā naz̤ar pānī meñ

[when that 'envy of the moon' goes and swims/floats in the water
her face looks like a Pari's, in the water]

Nevertheless, Mir created a second line so 'hot' that it turned into a verse. When the moon's rays are reflected in the water, then every wave seems to be illumined. The beloved is superior to the moon. Her body is more radiant even than the moon. Thus when she went down into the river, then every wave became as radiant as if there were moon-rays in it. The proof of this is that the beloved herself is in the water; and since the beloved is 'the envy of the moon', then for the waves to seem as if moon-rays were among them has a very great affinity.

The word gathī is devastating here. Because in it, in addition to the powerful oneness of the waves among themselves, there's also a subtle erotic suggestion. For the oneness of the rays and the waves, for them to be gathā huʾā is an extremely subtle/enjoyable idea. And on top of this, the image is both in motion, and stable. As an image of movement, the suggestion is again erotic-- that the beloved's body and the water are wrapped around each other like, so to speak, lover and beloved.

In the light of these subtleties, Jur'at's verse seems even more trivial. But in this 'ground' Jur'at has also pulled out some good verses, as will be described later in the discussion of the ghazal.

FWP:

SETS == SE
MOTIFS == EROTIC SUGGESTION
NAMES
TERMS == DOUBLE-GHAZAL; OPENING-VERSE

This ghazal has two opening-verses; that's why this second verse, chosen for SSA, has the structure of an opening-verse.

Since in the second line the word order has been rearranged in a potentially confusing way, let me just prosify it: pānī meñ lahar mahtāb se gathī huʾī uṭhtī thī . 'Envy of the moon' is of course a stock epithet for the beloved. The wave could be 'joined with the moon' for several possible reasons:

=Since the moon is envious of the beloved's beauty, the moon sends down rays into the water so that they can join with the waves in caressing the beloved's body (taking mahtāb se as 'from the moon').

=Since the beloved herself is a 'moon' even more radiant than the celestial moon, the waves around her shine the way they would in (ordinary) moonlight (taking mahtāb se as 'from the moon').

=Since the beloved is so desirable, the waves wrap themselves sensuously, and even sensually, around her 'moon'-like body (taking mahtāb se as 'with the moon').