श्री भगवानुवाच बहूनि मे व्यतीतानि जन्मानि तव चार्जुन। तान्यहं वेद सर्वाणि न त्वं वेत्थ परन्तप ॥

bahūni me vyatītāni janmāni tava chārjuna tānyahaṁ veda sarvāṇi na tvaṁ vettha parantapa

Many births have been left behind by Me and by thee, O Arjuna. I know them all, but thou knowest not thine, O Parantapa.

In plain words: Krishna answers that both he and Arjuna have been born many times before. Krishna remembers all his past lives, but Arjuna does not remember his.