3.43

एवं बुद्धेः परं बुद्ध्वा संस्तभ्यात्मानमात्मना ।
जहि शत्रुं महाबाहो कामरूपं दुरासदम् ॥

evaṃ buddheḥ paraṃ buddhvā saṃstabhyātmānam ātmanā
jahi śatruṃ mahābāho kāmarūpaṃ durāsadam

śrībhagavān (श्रीभगवान्) is speaking, and the last command of the chapter names the enemy and the place the blow comes from.

The verse

Thus having known the one higher than the buddhi, and having steadied the self by the self, kill the enemy, O mighty-armed one, the one whose form is desire and who is hard to approach.

नेपालीमा

यसरी बुद्धिभन्दा उच्चलाई जानेर र आत्माले आत्मालाई स्थिर राखेर, हे ठूला पाखुरा भएका, चाहनाको रूप भएको र नजिकिन गाह्रो शत्रुलाई मार।

Where it sits

The chapter opened by asking why act if knowledge is higher, and it ends with a kill: the enemy in the way of both is desire. The self above the buddhi is the place from which that enemy is struck, and the fight of 3.30 and this enemy are now on the same field.

Split: एवम् + बुद्धेः + परम् + बुद्ध्वा + संस्तभ्य + आत्मानम् + आत्मना + जहि + शत्रुम् + महा-बाहो + काम-रूपम् + दुरासदम्

evam + buddheḥ + param + buddhvā + saṃstabhya + ātmānam + ātmanā + jahi + śatrum + mahā-bāho + kāma-rūpam + durāsadam

Sanskrit, in depth

The words

देवनागरीWordGrammarSense
एवम्evamindeclinablethus. As the ladder just set it.
बुद्धेःbuddheḥablativethan the buddhi.
परम्paramaccusativethe one higher.
बुद्ध्वाbuddhvāgerund of budh (बुध्)having known.
संस्तभ्यsaṃstabhyagerund of sam-stambh (सम्-स्तम्भ्)having steadied.
आत्मानम्ātmānamaccusativethe self.
आत्मनाātmanāinstrumentalby the self.
जहिjahiimperative, 2nd singular of hā (हा)kill.
शत्रुम्śatrumaccusativethe enemy.
महा-बाहोmahā-bāhovocativeO mighty-armed one.
काम-रूपम्kāma-rūpamaccusativewhose form is desire. Agrees with śatrum (शत्रुम्).
दुरासदम्durāsadamaccusativehard to approach, hard to assail.

The phrases

एवम् बुद्धेः परम् बुद्ध्वा evaṃ buddheḥ paraṃ buddhvā picks up saḥ (सः) from 3.42 and tells him to know it. Thus having known the one higher than the buddhi.

संस्तभ्य आत्मानम् आत्मना saṃstabhya ātmānam ātmanā is the steadiness the blow requires. Having steadied the self by the self. संस्तभ्य + आत्मानम् saṃstabhya + ātmānam is saṃstabhyātmānam (संस्तभ्यात्मानम्). आत्मानम् + आत्मना ātmānam + ātmanā is ātmānam ātmanā (आत्मानमात्मना). One word is the object. The other is the means. Both are ātman (आत्मन्).

जहि शत्रुम् महाबाहो कामरूपम् दुरासदम् jahi śatruṃ mahābāho kāmarūpaṃ durāsadam is the kill. Kill the enemy, mighty-armed one, the one whose form is desire, hard to come near. This is prajahi (प्रजहि) of 3.41 without the prefix, and the enemy is the kāma (काम) of 3.37.

Sanskrit in this line

buddhvā (बुद्ध्वा) and saṃstabhya (संस्तभ्य) are both gerunds, "having done." buddhvā (बुद्ध्वा) has no prefix, so the ending is --tvā (त्वा). saṃstabhya (संस्तभ्य) has the prefix sam (सम्), so the ending is --ya (य). Same job. You choose by looking at the front of the verb, as with dṛṣṭvā (दृष्ट्वा) and upasaṅgamya (उपसङ्गम्य) in 1.2.

Say it back

What he knows, how he steadies himself, and whom he kills. If kāmarūpam (कामरूपम्) comes out as a second enemy beside śatrum (शत्रुम्), stay here. It describes the one enemy.