In his book What's Good About This News? (Westminster John Knox Press), David Bartlett tells this story:
"My wife and I have friends who have a wonderfully mixed family, mixed in part because one of their sons is their biological offspring and the other children are adopted. Not long ago they were explaining to the youngest child what it meant for him to be adopted - how he had been chosen, and waited for, and welcomed with joy. As part of the story they also had to explain that Mark, the brother, was their child biologically. When they had finished explaining what it meant to say that Tommy was adopted, he cried out: 'Oh, that's wonderful. Can't we adopt Mark too?'
"Paul believes that God has adopted us all, Jew and Gentile, male and female, slave and free, in Jesus Christ. And Paul declares the wonder of that adoption." (Gal. 4:4-7)
(Bartlett's book is an expansion of his Lyman Beecher Lectures on Preaching, delivered at Yale in 2001. In the book the Yale professor deals with the meaning of good news in each of the Gospels and in Galatians; the book also includes five representative sermons.)