If you send a servant to make a fire for you, and he goes and lays some green wood together and puts a few coals underneath, this is not to make a fire for you. He must either get dry wood, or he must blow until it burns and is fit for use.
So when your hearts are unfit, when they are like green wood, when you come to warm them and to quicken them by prayer to God, it may be you post over this duty, and leave your hearts as cold and distempered as they were before. My beloved, this is not to perform this duty. The duty is effectually performed when your hearts are wrought upon by it, and when they are brought to a better tune and temper than they were before.
If you find sinful lusts, your business there is to work them out by prayer, to reason the matter, to expostulate the thing before the Lord, and not to give over until you have set all the wheels of your soul right, until you have made your hearts perfect with God. And, if you find your hearts cleaving too much to the world, you must wean them and take them off. If you find a deadness and unaptness, an indisposition in you, you must lift up your souls to the Lord and not give over until you are quickened. And this is to perform the duty in such a manner as the Lord accepts, otherwise it is hypocritical performance; for this is hypocrisy, when a man is not willing to let the duty go altogether, nor yet is willing to perform it fervently, and in a quick and zealous manner.
John MacArthur, Alone With God, Includes Indexes. (Wheaton, Ill.: Victor Books, 1995).