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 be unprofitable servants.