John 3:5

of water and of the Spirit--A twofold explanation of the "new birth," so startling to Nicodemus. To a Jewish ecclesiastic, so familiar with the symbolical application of water, in every variety of way and form of expression, this language was fitted to show that the thing intended was no other than a thorough spiritual purification by the operation of the Holy Ghost. Indeed, element of water and operation of the Spirit are brought together in a glorious evangelical prediction of Ezekiel (Eze 36:25-27), which Nicodemus might have been reminded of had such spiritualities not been almost lost in the reigning formalism. Already had the symbol of water been embodied in an initiatory ordinance, in the baptism of the Jewish expectants of Messiah by the Baptist, not to speak of the baptism of Gentile proselytes before that; and in the Christian Church it was soon to become the great visible door of entrance into "the kingdom of God," the reality being the sole work of the Holy Ghost (Tit 3:5).

— Jamieson-Fausset-Brown Commentary (public domain)