JI Packer presents adoption as the highest blessing of the gospel:
What is a Christian? The richest answer I know is that a Christian is one who has God as his Father. If you want to know how well someone 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 the Gospel very well at all… adoption is the highest blessing of the Gospel
Phil Wilthew
From the book “Developing Prophetic Culture”