Why do we fast? In fact, why do we do anything we do? Our motivations matter but we tend to not be aware of them. Isaiah, who is speaking on behalf of God, will help us get a handle on it.
Isaiah 58:6 Is not this the fast that I choose: to loose the bonds of wickedness, to undo the straps of the yoke, to let the oppressed go free, and to break every yoke?