John Gill

Nicodemus saith unto him,.... Understanding him of a natural birth, to be repeated: how can a man be born when he is old? as it seems by this, he himself now was: can he enter the second time into his mothers womb, and be born? the Ethiopic version adds, "again"; and the Arabic version, "and then be born"; this he urges, as absurd, impracticable, and impossible; and which shows him to have been as yet a natural man, who could not receive nor discern spiritual things.