"Adoption, by its very nature, is an act of free kindness to the person adopted. If you become a father by adopting a son or daughter, you do so because you choose to, not because you are bound to. Similarly, God adopts because he chooses to. He has no duty to do so. He need not have done anything about our sins except punish us as we deserved. But he loved us; so he redeemed us, forgave us, took us as his sons and daughters and gave himself to us as our Father."
J.I. Packer, Knowing God pg.215