You and I, it may be said, know little about heaven. Our notions of heaven may be very dim and unclear. But at all events, I suppose we are agreed in thinking that heaven is a very holy place—that God is there—and Christ is there—and saints and angels are there—that sin is not there in any shape—and that nothing is said, thought, or done, which God does not like. Only let this be granted, and then I think there can be no doubt the great majority of professing Christians are as little fit for heaven as a bird for swimming beneath the sea, or a fish for living upon dry land. And what is it they need in order to make them fit to enjoy heaven? They need to be regenerated or born again.
~ J.C. Ryle
Tract: Are You Regenerate?