Ephesians 5:1 Therefore be imitators of God, as beloved children.

John Murray: Adoption, as the term closely implies, is an act of transfer from an alien family into the family of God himself.  This is surely the apex of grace and privilege

Donald Grey Barnhouse:  the Christian is far more than a guest with God. 

Thomas Watson:  God has made his children, by adoption, nearer to himself than the angels.  The angels are the friends of Christ; believers are his members. 

JI Packer: Our first point about adoption is that it is the highest privilege that the gospel offers. In adoption, God takes us into his family and fellowship—he 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 [justification] is a great thing, but to be loved and cared for by God the Father [adoption] is a greater.

Thomas Watson:  Since God has a Son of his own, and such a Son, how wonderful God’s love in adopting us!  We needed a Father, but He did not need sons.

 John Calvin:  We can only begin an upright course of life when God, of his good pleasure, adopts us into his family.