Martin Luther dealt with the matter of simplicity in the most profoundly practical way in his book, The Freedom of a Christian. What he saw in acutely sharp focus was that the liberty of the gospel sets us free to serve our neighbor with singleness of purpose. If our salvation is by grace alone, we no longer need to keep juggling a myriad of religious duties to get right with God. We are free from constantly taking our own spiritual temperature. Our freedom from sin allows us to serve others. Before all our serving was for our benefit, a means to somehow get right with God. Only because the grace of God has been showered upon us are we enabled to give that same grace to others.
Luther expressed this thesis in his famous paradox, A Christian is a perfectly free lord of all subject to none. A Christian is a perfectly dutiful servant of all subject to all. Through the grace of God alone and not by any work of righteousness of our part, we come into the glorious liberty of the gospel. We are all lords and kings, and priests, as Luther put it. We are set free from the law of sin and death. But this freedom is not for our sake alone, it is also a freedom to serve others. Until we are righteous we cannot really do righteous deeds, no matter how hard we try. Luther said, "Good works do not make a good man, but a good man does good works. Evil works don't make a wicked man, but a wicked man does evil works." Lets illustrate this matter in a simple way. A poor artist may paint many pictures, but he will not paint any good pictures. An inferior contractor may build many homes, but he will not construct any good homes.
The person who is still bound to sin and enslaved to others is not free to truly love his neighbor. A moments reflection on our part confirms the truth of Luther's insight. If we are still in bondage to sin our serving will flow out of that center. We will not have the single eye that gives light to all we do. Pride and fear and manipulation will control our actions. We will not be free to serve our neighbor in simplicity if we are still in bondage to others serving will flow out of that center. We will be controlled by a desire to impress them or receive their help. Without gospel liberty we will forever measure who we are by the yardstick of others. We will not be free to serve our neighbor in simplicity. But once the grace of God has broken into our lives we are free. When we are free from the control of our neighbor, we are able to obey God. And as we obey God with a single heart we are given a new power and desire to serve our neighbor from whom we are now free. We have become servants of our neighbors and yet lords of all. We know simplicity of life. Luther concludes, "A Christian lives not in himself, but in Christ and his neighbor. Otherwise he is not a Christian."
(Excerpt from Richard Foster, Freedom of Simplicity)