Faith is belief unto action. Action is what distinguishes faith from mere wishing. Desire can come passively, but actions are required to both discover and walk the path to obtain outcomes.
The purpose of faith is to obtain the outcomes that are obtained through it. While desire and reason form motivation, the entire purpose of desire and reason is to motivate someone to act in ways that are different or more difficult than what they would have done otherwise. Outcomes are completely obtained through actions.
Faith is a principle of power in that it yields the actions that result in outcomes that would otherwise not come to pass:
And Christ hath said: If ye will have faith in me ye shall have power to _do_ whatsoever thing is expedient in me. (Moroni 7:33)
If you want to exercise faith, you must counsel with God to find out what action is required. Every outcome in this universe occurs according to specific preconditions that are known to God:
20 There is a law, irrevocably decreed in heaven before the foundations of this world, upon which all blessings are predicated—
21 And when we obtain any blessing from God, it is by obedience to that law upon which it is predicated. (D&C 130)
14 I, the Lord, stretched out the heavens, and built the earth, my very handiwork; and all things therein are mine. 15 And it is my purpose to provide for my saints, for all things are mine.
16 But it must needs be done in mine own way.... (D&C 104)
The action step of the faith process is all about discovering, executing, and improving the actions that yield the outcomes you desire.