“If you want to judge how well a person understands Christianity, find out how much he makes of the thought of being God’s child, and having God as his Father. If this is not the thought that prompts and controls his worship and prayers and his whole outlook on life, it means that he does not understand Christianity very well at all.
"For everything that Christ taught, everything that makes the New Testament new, and better than the Old, everything that is distinctively Christian as opposed to merely Jewish, is summed up in the knowledge of the Fatherhood of God. 'Father' is the Christian name for God. … Our understanding of Christianity cannot be better than our grasp of adoption...
“Justification is a forensic idea, conceived in terms of law, and viewing God as judge… Adoption is a family idea, conceived in terms of love, and viewing God as father. In adoption, God takes us into His family and fellowship, and establishes us as His children and heirs. Closeness, affection and generosity are at the heart of the relationship. To be right with God the judge is a great thing, but to be loved and cared for by God the father is greater”
(J. I. Packer, from Knowing God)