. . . only he who believes is obedient, and only he who is obedient believes. It is quite unbiblical to hold the first proposition without the second. We think we understand when we hear that obedience is possible only where there is faith. Does not obedience follow faith as good fruit grows on a good tree? First, faith, then obedience. If by that we mean that it is faith which justifies, and not the act of obedience, all well and good, for that is the essential and unexceptional presupposition of all that follows. If, however, we make a chronological distinction between faith and obedience, and make obedience subsequent to faith, we are divorcing the one from the other–and then we get the practical question, when must obedience begin? Obedience remains separated from faith. From the point of view of justification it is necessary thus to separate them, but we must never lose sight of their essential unity. For faith is only real when there is obedience, never without it, and faith only becomes faith in the act of obedience.
-Dietrich Bonhoeffer, The Cost of Discipleship