"Faith alone saves, but a faith that saves is never alone."
True faith will always be followed by action. This doesn't mean that someone with true faith will be perfect. What it does mean, is that someone with true faith will desire to be perfect. They will desire to be free from sin, they will have a drive for purity.
God will not release us to walk and live with full authority if we are not striving to live in purity. To go out in God's authority means we go out representing Him. He is pure, therefore to represent Him, we must be pure. He is holy, therefore to represent Him, we must be holy. It is that simple. If we are constantly living in sin then we are not representing Him. If we conform ourselves to the ways of this world then we are not representing Him.
If we want to walk in the power that comes with God's authority then we must learn to represent Him in our actions, thoughts, and words. We must separate ourselves from the ways of the world and allow God to transform us into His image. Jesus, in John 17, said that though He has sent us into the world we are not "of this world." The church today often seems to be attempting to adopt the ways of the world in order to draw them in, but what the world needs is a church that adopts the ways of their Lord. We need to show people what makes us different, show them why they should listen to us, why They need Jesus. It is only through allowing ourselves to be transformed into His image that we will be successful in drawing in the people who need Him.
To live a pure and holy life does not mean to be perfect. On the contrary, to live a pure and holy life means to recognize our imperfection and to draw on God's perfection. It means that we recognize and accept the full grace of God in our lives and have allowed that grace to transform us into His likeness. It is in this transformation that we begin to walk in the authority that God has given us.