From Luther's Heidelberg Disputation

1. fulfill everything through him since he was made ours through faith.
2. Actually one should call the work of Christ an acting work (operans) and our work an accomplished work (operatum), and thus an accomplished work pleasing to God by the grace of the acting work.
   Since Christ lives in us through faith so he arouses us to do good works through that living faith in his work, for the works which he does are the fulfillment of the commands of God given us through faith. If we look at them we are moved to imitate them. For this reason the Apostle says, »Therefore be imitators of God, as beloved children«(Eph. 5:1). Thus deeds of mercy are aroused by the works through which he has saved us, as St. Gregory says: »Every act of Christ is instruction for us, indeed, a stimulant.« If his action is in us it lives through faith, for it is exceedingly attractive according to the verse,»Draw me after you, let us make haste« (Song of Sol. 1:4) toward the fragrance »of your anointing oils« (Song of Sol. 1:3),