Here is the mechanism behind the reassurance. In the new life, the yogi does not start from zero. The buddhi-samyoga — the inner connection, the accumulated understanding — from the previous life returns. The seeker picks up exactly where the last life left off.
And then something remarkable: 'yatate cha tato bhuyah' — from that point, the yogi strives even harder. The momentum is not just preserved. It increases. Each life builds on the last, the way a river grows wider and stronger as it flows toward the sea.
Krishna addresses Arjuna here as 'Kurunandana' — joy of the Kurus. There is affection in the name. The message is warm: your efforts are not written on sand. They are carved into the soul. They travel with you.