वेदाहं समतीतानि वर्तमानानि चार्जुन। भविष्याणि च भूतानि मां तु वेद न कश्चन ॥

vedāhaṁ samatītāni vartamānāni chārjuna bhaviṣhyāṇi cha bhūtāni māṁ tu veda na kaśhchana

I know the beings that are past, that are present, that are to come, O Arjuna, but no one knoweth Me.

In plain words: Krishna tells Arjuna that he knows every being from the past, present and future, but no one truly knows him.