John 3:3

Except, &c.--This blunt and curt reply was plainly meant to shake the whole edifice of the man's religion, in order to lay a deeper and more enduring foundation. Nicodemus probably thought he had gone a long way, and expected, perhaps, to be complimented on his candor. Instead of this, he is virtually told that he has raised a question which he is not in a capacity to solve, and that before approaching it, his spiritual vision required to be rectified by an entire revolution on his inner man. Had the man been less sincere, this would certainly have repelled him; but with persons in his mixed state of mind--to which Jesus was no stranger (Joh 2:25) --such methods speed better than more honeyed words and gradual approaches. a man--not a Jew merely; the necessity is a universal one. be born again--or, as it were, begin life anew in relation to God; his manner of thinking, feeling, and acting, with reference to spiritual things, undergoing a fundamental and permanent revolution. cannot see--can have no part in (just as one is said to "see life," "see death," &c.). the kingdom of God--whether in its beginnings here (Luk 16:16), or its consummation hereafter (Mat 25:34; Eph 5:5).

— Jamieson-Fausset-Brown Commentary (public domain)