Regeneration is a secret act of God in which He imparts spiritual life to us; sometimes called being born again.
Regeneration
...ye must be born again
But because of his great love for us, God, who is rich in mercy, made us alive [quickened us] with Christ even when we were dead in transgressions– it is by grace you have been saved. Ephesians 2:4-5
It is the Spirit who gives life; the flesh is of no avail. The words that I have spoken to you are spirit and life. But there are some of you who do not believe." (For Jesus knew from the beginning who those were who did not believe, and who it was who would betray him.) And he said, "This is why I told you that no one can come to me [i.e. believe in me] unless it is granted him by the Father." John 6:63-65
We don't develop or evolve into a new creature: it is a miracle ex nihilo.
"You have been born anew, not of perishable seed but but of imperishable, through the living and abiding word of God..." (1 Peter 1:23,25)
"Everyone who believes that Jesus is the Christ has been born of God" (1 John 5:1 )
"...the first effect of the power of God in the heart in regeneration is to give the heart a Divine taste or sense; to cause it to have a relish of the loveliness and sweetness of the supreme excellency of the Divine nature. - Jonathan Edwards
I say that man, before he is renewed into the new creation of the Spirit's kingdom, does and endeavours nothing to prepare himself for that new creation and kingdom, and when he is re-created has does and endeavors nothing towards his perseverance in that kingdom; but the Spirit alone works both blessings in us, regenerating us, and preserving us when regenerate, without ourselves..." -Martin Luther (Bondage of the Will pg. 268)
"Indeed the Word of God is like the sun, shining upon all those to whom it is proclaimed, but with no effect among the blind. Now, all of us are blind by nature in this respect... Accordingly, it cannot penetrate into our minds unless the Spirit, as the inner teacher, through his illumination makes entry for it." (Calvin's Institutes 3.2.34.)
"The Reformers, and particularly John Calvin, stressed the way the objective, written Word and the inner, supernatural ministry of the Holy Spirit work together, the Holy Spirit illuminating the Word to God's people. The Word without the illumination of the Holy Spirit remains a closed book." - James M Boice
"Faith in the living God and his Son Jesus Christ is always the result of the new birth, and can never exist except in the regenerate. Whoever has faith is a saved man." - C.H. Spurgeon from His sermon Faith and Regeneration
"If salvation is the implantation of a new, infinite life in the soul, it must be a work of God. Self-caused effects can never rise above the character or qualities of their cause. "Flesh gives birth to flesh but the Spirit gives birth to Spirit," Jesus told Nicodemus. This saving grace cannot be caused by the creature, it can only come from God." - John Hannah (To God be the Glory pg. 34, 35)
The inward offer is a kind of spiritual enlightenment, whereby the promises are presented to the hearts of men, as it were, by an inward word." - William Ames
"...the Holy Spirit does not save people in a void, but, as we cast forth the seed of the gospel, He quickens us through the Word of truth. The Holy Spirit, germinates the seed, so to speak, quickening us though the Word. The seed does not work on its own, it requires the prior blessing of God. "...we know, brothers loved by God, that he has chosen you because our gospel came to you not only in word, but also in power and in the Holy Spirit and with full conviction." (1 Thess 1:4, 5)
Copied from Steve Camp's blogsite