1 John 3:9 Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.
Here are the verses about the faithful remnant of Israel that will enter the earthly kingdom that Nicodemus should have known;
Eze 36:24 For I will take you from among the heathen, and gather you out of all countries, and will bring you into your own land.
Eze 36:25 Then will I sprinkle clean water upon you, and ye shall be clean: from all your filthiness, and from all your idols, will I cleanse you.
Eze 36:26 A new heart also will I give you, and a new spirit will I put within you: and I will take away the stony heart out of your flesh, and I will give you an heart of flesh.
Eze 36:27 And I will put my spirit within you, and cause you to walk in my statutes, and ye shall keep my judgments, and do them.
John was writing to those believing of Israel that were waiting for the nation to receive the kingdom.