Jesus answered and said to him, "Most assuredly, I say to you, unless one is born again, he cannot see the kingdom of God.

"Do not marvel that I said to you, 'You must be born again.' The wind blows where it wishes, and you hear the sound of it, but cannot tell where it comes from or where it goes. So is everyone who is born of the Spirit."
John 3:3, 7-8

Even the smallest sins have marred what we are naturally. God is perfectly righteous and holy, so fixing up a sin-stained heart is not an option. God chooses instead to complete a work of new birth in the hearts of those who come to Him for forgiveness. "Born-again" Christians are not one sort or denomination of Christians; they are the only type of Christians, according to Jesus.