This is part of my commentary series on The 39 Articles of Religion. Article 14 states:
XIV. Of Works of Supererogation
Voluntary Works besides, over, and above, God’s Commandments, which they call Works of Supererogation, cannot be taught without arrogancy and impiety: for by them men do declare, that they do not only render unto God as much as they are bound to do, but that they do more for his sake, than of bounden duty is required: whereas Christ saith plainly, When ye have done all that are commanded to you, say, We are unprofitable servants.
By the time of the Reformation, a doctrine of “works of supererogation” had developed. Supererogation, loosely translated, means “going above and beyond.” Roman Catholic teaching put forth the idea that some good works a person can undertake are in fact beyond the ordinary demands of the law of Christ. A classic example of a work of supererogation was making (and following through on) vows of life-long celibacy. God does not ordinarily demand such a sacrifice, so to do so willingly out of love and devotion for God was considered a good work above the norm. Appeals were made to Ephesians 6:8, which states “whatever good anyone does, this he will receive back from the Lord.”
But the Reformers took issue with this doctrine. As this Article quotes, “when you have done all that you were commanded, say, ‘We are unworthy servants; we have only done what was our duty’” (Luke 17:10). This is consistent with the conclusions drawn in the previous three Articles: we are justified by Christ’s merits, not our own (Article 11), the good works we do only proceed from God’s grace of justification (Article 12), and we cannot do any good works before we are justified anyway (Article 13). Thus it is fruitless to attempt to discern forms of good works that go “above” the standards of God, as there is no efficacy in any work, however good, toward our justification.