A.T. Robertson Commentary John 3:6

"That which is born of the flesh is flesh; and that which is born of the Spirit is spirit." — John 3:6 (ASV)

That which is born (το γεγεννημενον). Perfect passive articular participle. The sharp contrast between flesh (σαρξ) and Spirit (πνευμα), drawn already in 1:13, serves to remind Nicodemus of the crudity of his question in 3:4 about a second physical birth.