Here’s a description from Bob Kauflin’s blog:
Son’s and Daughters came out of a perceived lack of songs that help us meditate on the unfathomable love God has shown us in adopting us through Jesus Christ (Eph. 1:5). We are now part of God’s family – in Christ we will forever be the objects of God’s particular and passionate mercy and love. We are not only forgiven, we are co-heirs with Christ, and never again have to doubt God’s care for us. That biblical reality, rather than leaving us focused on ourselves, drives us once again to proclaim the greatness of the God whose grace turns hopeless rebels into the precious children.
“And because you are sons, God has sent the Spirit of his Son into our hearts, crying, ‘Abba! Father!” (Gal. 4:6)