6.43

तत्र तं बुद्धिसंयोगं लभते पौर्वदेहिकम् ।
यतते च ततो भूयः संसिद्धौ कुरुनन्दन ॥

tatra taṃ buddhisaṃyogaṃ labhate paurvadehikam
yatate ca tato bhūyaḥ saṃsiddhau kurunandana

Kṛṣṇa (कृष्ण) is still speaking. tatra (तत्र) is the birth of 6.41 or 6.42.

The verse

There he obtains that joining with understanding which belonged to the former body, and he strives again from that point toward perfection, joy of the Kurus.

नेपालीमा

त्यहाँ उसले अघिल्लो शरीरको बुद्धिसँगको त्यो जोडाइ पाउँछ। अनि त्यहीँबाट फेरि सिद्धितिर प्रयास गर्छ, हे कुरुहरूको आनन्द।

Where it sits

The new birth is not a start from nothing. The understanding he had joined once comes back, and the striving of 6.36 resumes. 6.44 says he is carried by that former practice even when he is not willing it.

Split: तत्र + तम् + बुद्धि-संयोगम् + लभते + पौर्वदेहिकम् + यतते + च + ततः + भूयः + संसिद्धौ + कुरुनन्दन

tatra + tam + buddhi-saṃyogam + labhate + paurvadehikam + yatate + ca + tataḥ + bhūyaḥ + saṃsiddhau + kurunandana

Sanskrit, in depth

The words

देवनागरीWordGrammarSense
तत्रtatraindeclinablethere.
तम्tamaccusative singularthat.
बुद्धि-संयोगम्buddhi-saṃyogamaccusative singularthe joining with understanding.
लभतेlabhatepresent, 3rd singular, middlehe obtains.
पौर्वदेहिकम्paurvadehikamaccusative singularbelonging to the former body. Agrees with buddhisaṃyogam (बुद्धिसंयोगम्).
यततेyatatepresent, 3rd singular, middlehe strives.
चcaindeclinableand.
ततःtataḥindeclinablefrom that, then.
भूयःbhūyaḥindeclinableagain, further.
संसिद्धौsaṃsiddhaulocative singulartoward perfection, in the attainment.
कुरुनन्दनkurunandanavocativejoy of the Kurus. Arjuna.

The phrases

तत्र तम् बुद्धिसंयोगम् लभते पौर्वदेहिकम् tatra tam buddhisaṃyogaṃ labhate paurvadehikam is what meets him in the new birth. He obtains that joining with understanding which belonged to the former body. The effort was not erased.

yatate ca tataḥ bhūyaḥ saṃsiddhau (यतते च ततः भूयः संसिद्धौ) is what he does with it. He strives on from there, further, toward perfection.

Sanskrit in this line

paurvadehika (पौर्वदेहिक) is an adjective built from pūrvadeha (पूर्वदेह), "the former body." The first vowel is strengthened, pūrva (पूर्व) becoming paurva (पौर्व), and --ika (इक) makes "belonging to." The locative saṃsiddhau (संसिद्धौ) marks the goal he strives toward. yatate (यतते) is the verb whose participle yatatā (यतता) was the successful man in 6.36, and whose negative ayatiḥ (अयतिः) was the man who fell in 6.37.

Say it back

What he obtains from the former body, and what he does again. If paurvadehikam (पौर्वदेहिकम्) drops out, the new birth has no memory of the old effort.