A good exposition, Helen. Another view:

Article XIV of the 39 Articles of Religion, adopted by the Church of England at the Reformation, reads as follows:

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.

Those old divines didn't mince words. (Some of the other Articles are more blunt and uncomplimentary.) Of course, those were the days when people killed each other, often in most unpleasant ways, over niceties of dogma.