Keller's basic thesis is that we have misnamed the parable of the prodigal son and caused the word prodigal to morph into meaning “wayward.” In actuality, prodigal means recklessly extravagant, which defines God's relationship with us; scripture calls the parable “the parable of the two sons,” since there is an elder and younger brother. With that as background, I present you with the first excerpt:
Jesus' teaching consistently attracted the irreligious while offending the Bible-believing, religious people of his day. However, in the main our churches today do not have this effect. The kind of outsiders Jesus attracted are not attracted to contemporary churches, even our most avant-garde ones. We tend to draw conservative, buttoned-down, moralistic people. The licentious and liberated or the broken and marginal avoid church. That can only mean one thing. If the preaching of our ministers and the practice of our parishioners doesn't have the same effect on people that Jesus had, then we must not be declaring the same message that Jesus did. If our churches aren't appealing to younger brothers, they must be more full of elder brothers than we'd like to think.—Timothy Keller, The Prodigal God, pages 15-16
Ouch! Many of us (me included) started out as younger brothers whom Jesus went looking for. Once he found us, he cleaned us up. Problem is, we think we cleaned ourselves up and we look down on the very people we used to be—and still would be but for God's mercy and grace being manifested to us and transforming us.