A Biblical scholar has written, “Few ideas in New Testament studies produce higher levels of agreement than the notion that Paul’s letter to Philemon has little or no theological substance.” All that statement says is that a lot of smart people are really quite dumb.
This book may not tease out the doctrine of redemption, but I dare you to find another one that works it in so well. Only if your Christianity is all brain and no heart or limb can you say such a thing. Only if you approach the Bible with an academic processor and not an ardent heart, could you be so blind.
Theology here is worked out further than many care to go. It is worked pass the brain, into the heart, and out the hands. This is theology well digested and carried through the body. This is what it looks like when the blood of Jesus gets into our bloodstream. Here you see the doctrines of union with Christ, adoption in Christ, the family of God, redemption, and forgiveness as they take root in the heart of man and produce the fruit of the Spirit. Philemon is applied theology.
Just as the aforementioned doctrines are light in a dark world, so too, the life they produce in man is contrary to this culture. The gospel is foolishness to this world all the way down and all the way out. Thus, Philemon just might have been the most shocking little letter in the ancient world. If we too so ingrain the truth of Christ and his redemption, it is still surely so today.