Bhagavad Gita Chapter 8, Verse 15

मामुपेत्य पुनर्जन्म दु:खालयमशाश्वतम् | नाप्नुवन्ति महात्मान: संसिद्धिं परमां गत: ||

mām upetya punar janma duḥkhālayam aśāśvatam nāpnuvanti mahātmānaḥ saṁsiddhiṁ paramāṁ gatāḥ

Having attained Me, the great souls do not undergo rebirth in this transient world, which is full of miseries, as they have reached the highest perfection.

Krishna describes the result of attainment: 'Mam upetya'—having attained (upetya) Me (mam), 'punar janma duhkhalayam ashashvatam na apnuvanti'—the great souls (mahatmanah) do not undergo (na apnuvanti) rebirth (punar janma) in this transient (ashashvatam) world, which is full of miseries (duhkhalayam). 'Samsiddhim paramam gatah'—as they have reached (gatah) the highest (paramam) perfection (samsiddhim). This is the liberation: when you attain Krishna through constant remembrance, you don't take birth again in the material world. The material world is transient and full of miseries—but once you attain Krishna, you're free from it. This is the highest perfection—liberation from the cycle of birth and death. Great souls who attain Krishna don't return to the material world—they've reached the highest goal.