Sanskrit
तत्र तं बुद्धिसंयोगं लभते पौर्वदेहिकम् । यतते च ततो भूयः संसिद्धौ कुरुनन्दन ॥
tatra taṃ buddhisaṃyogaṃ labhate paurvadehikam yatate ca tato bhūyaḥ saṃsiddhau kurunandana
Translation
There he recovereth the characteristics belonging to this former body, and with these he again laboureth for perfection, O joy of the Kurus.
Annie Besant · The Bhagavad-Gita, translated by Annie Besant (4th ed., 1922) — Wikisource · Public Domain
Explanation
This is the mechanism’s payoff and the direct answer to Arjuna’s fear of total loss in verses 37–38: the connection with understanding built up in the previous life carries forward into the new one. Nothing has to be relearned from zero — the new effort resumes from where the old one left off.