The Gospel of the Apostle John is the gospel of the spirit, of those who are born again, it is the gospel of the spiritual man and of the eternal life. This is the only gospel that narrates the dialogue between Jesus and the Pharisee Nicodemus, about the spiritual birth.
Although the Gospels are tractates about God from the Christian perspective, that is to say treatises of Theology, from the point of view of philosophy the Gospel of John is unique. This gospel describes the Gnosis, that is, in what consist the spiritual rebirth. The word Gnosis in Greek means knowledge, is the term used in philosophy to describe the birth of the spirit.
The wind in the Gospel of John is compared with the Holy Spirit:

"The wind blows where
it wishes, and you hear
the sound of it but,
cannot tell where it
comes from and where
it goes. So is everyone
who is born of the
spirit." John 3:8

A nature is towards what the being tends in his own development Aristotle explains in his book Metaphysics.The nature of the worm is the butterfly, the nature of the seed is the plant that bears fruit. In the same way the nature of man is the conformity to God.
The conformity to God requires an interior transformation, a second birth. Through this second birth we receive the essence of God. When we are born from the spirit our essence is transformed, by the essence of God.
Recall that the essence of man is the reason and the essence of God is the wisdom. We can not attain grace through reason, we need a special help, and this special assistance is the second birth, also known as "Gnosis".
The Bible teaches us the difference between soul and spirit. When the soul prevails, we have the rational man, when the spirit prevails we have the spiritual man. The second birth is the transformation of the rational man in the spiritual man, a change of essence. Remember Pentecost in Acts of the Apostles 2
Through the Gnosis we contemplate the divine truths and we participate in the joy of God. The second birth is a potential jump, it is a "push up", we are kids again, the eye of the mind is activated, we learn to trust in the senses of the spirit: the intuition, the inspiration, the creativity, the good discernment. Constancy, the gift of serenity is the way to the second birth, as the Parable of the sower teaches.
In the Roman Catholic Apostolic religion the new birth is represented in the sacrament of confirmation, where the adult person is declared, that is, confirmed in the faith, and in possession of the 7 gifts of the Holy Spirit.