As bad as it might be to destroy a creature made in God's image, it might be very much worse to be creating them after images of one's own.
It's all kinds of these profound things crashing on you when your child arrives into the world. It's like you've met your reason to live.
Here he tells us that the new birth is first of all 'not of blood'. You don't get it through the blood stream, through heredity. Your parents can give you much, but they cannot give you this.