Keller fleshes out a fuller understanding of human sinfulness and lostness than is often seen in sermons preached or works written about this parable. Most preachers and authors focus on the younger brother and his licentious living. However, Keller focuses on the elder brother as well, pointing out the equally sinful lifestyle and lost condition of religious folks. He leaves no wiggle room for the elder brothers (i.e. religiously lost) who "obey God to get things" (p. 42), going so far as to assert that "religious and moral people can be avoiding Jesus as Savior and Lord as much as the younger brothers who say they don't believe in God and define right and wrong for themselves" (p. 43). This caught my attention, for I was that kind of elder brother who was avoiding submitting my life to Christ through a superficial obedience to external commands largely so that I can "get things" from God: peace, decent job, respect, etc.
This book caused me to love the grace of God and the saving work of Christ all the more. Keller gave me a new insight concerning this parable that I had never noticed. In the first two parables in Luke 15--the parable of the lost sheep and the parable of the lost coin--someone goes out looking for what is lost. In the prodigal son, no one goes looking. Why? Keller points back to the story of Cain and Abel, where Cain should have been his brother's keeper. The elder brother in this parable should have been out searching for his brother, but "by putting a flawed elder brother in the story, Jesus is inviting us to imagine and yearn for a true one" (p. 84).
Thankfully, Christ did enter this world and take on human flesh to rescue those who put their trust in Him alone by grace through faith, for "we will never stop being younger brothers or elder brothers until we acknowledge our need, rest by faith, and gaze in wonder at the work of our true elder brother, Jesus Christ" (p. 89).
So, please take some time and read this book. If you're in the Chatsworth, GA area feel free to drop by the church so that I can gladly loan it to you.
Here are some more quotes from the work:
"Careful obedience to God's law may serve as a strategy for rebelling against God" (p. 37).
"If you've become a Christian out of being an elder brother, you can even more easily slide back into elder-brother attitudes and spiritual deadness. If you have not grasped the gospel fully and deeply, you will return to being condescending, condemning, anxious, insecure, joyless, and angry all the time" (p. 70).
"It's not the repentance that causes the father's love, but rather the reverse" (p. 74).
"What must we do, then, to be saved? To find God we must repent of the things we have done wrong, but if that is all you do, you may remain just an elder brother. To truly become Christians we must also repent of the reasons we ever did anything right" (p. 78).