Article 24: Man’s Sanctification and Good Works.
We believe that this true faith, being wrought in man by the hearing of the Word of God and the operation of the Holy Ghost, doth regenerate and make him a new man, causing him to live a new life, and freeing him from the bondage of sin. Therefore it is so far from being true that this justifying faith makes men remiss in a pious and holy life, that on the contrary, without it they would never do anything out of love to God, but only out of self-love or fear of damnation. Therefore it is impossible that this holy faith can be unfruitful in man; for we do not speak of a vain faith, but of such a faith which is called in Scripture a faith that worketh by love, which excites man to the practice of those works which God has commanded in His Word.
These works, as they proceed from the good root of faith, are good and acceptable in the sight of God, forasmuch as they are all sanctified by His grace; howbeit they are of no account towards our justification. For it is by faith in Christ that we are justified, even before we do good works; otherwise they could not be good works, any more than the fruit of a tree can be good before the tree itself is good.
Therefore we do good works, but not to merit by them (for what can we merit?) nay, we are beholden to God for the good works we do, and not He to us, since it is He that worketh in us both to will and to do of His good pleasure. Let us therefore attend to what is written: When ye shall have done all those things which are commanded you, say, we are unprofitable servants; we have done that which was our duty to do. In the meantime we do not deny that God rewards our good works, but it is through His grace that He crowns His gifts. 
Moreover, though we do good works, we do not found our salvation upon them; for we can do no work but what is polluted by our flesh, and also punishable; and although we could perform such works, still the remembrance of one sin is sufficient to make God reject them. Thus, then, we would always be in doubt, tossed to and fro without any certainty, and our poor consciences continually vexed, if they relied not on the merits of the suffering and death of our Savior.