In John 3:5, Jesus tells Nicodemus that to enter the kingdom one must be "born of water and the Spirit". How is this phrase understood? Is it a single construct (i.e. one birth of both water and Spirit)? Or are two births in view (one of water and one of Spirit)? And what does it mean to be born of water?
One of the earliest of the Church Fathers to enunciate clearly and unambiguously the doctrine of baptismal regeneration ("the idea that salvation happens at and by water baptism duly administered") was Cyprian (c. 200 – 258): "While he attributed all the saving energy to the grace of God, he considered the 'laver of saving water' the instrument of God that makes a person 'born again', receiving a new life and putting off what he had previously been. The 'water of new birth' animated him to new life by the Spirit of holiness working through it."
In the early days of his conversion he wrote an Epistola ad Donatum de gratia Dei and the Testimoniorum Libri III that adhere closely to the models of Tertullian, who influenced his style and thinking. Cyprian described his own baptism in the following words:
When I was still lying in darkness and gloomy night, I used to regard it as extremely difficult and demanding to do what God's mercy was suggesting to me... I myself was held in bonds by the innumerable errors of my previous life, from which I did not believe I could possibly be delivered, so I was disposed to acquiesce in my clinging vices and to indulge my sins....
But after that, by the help of the water of new birth, the stain of my former life was washed away, and a light from above, serene and pure, was infused into my reconciled heart... a second birth restored me to a new man. Then, in a wondrous manner every doubt began to fade.... I clearly understood that what had first lived within me, enslaved by the vices of the flesh, was earthly and that what, instead, the Holy Spirit had wrought within me was divine and heavenly.http://control-avles-blogs.blogspot.com/2014/06/anabaptist-bread-with-catholic-leaven.html
— Cyprian, Ad Donatum, 3-4