He [Christ] only is sufficient for this work; all ways and means without him are as a thing of nought; and he is the great efficient of it,—he works in us as he pleases.
In vain do men seek other remedies; they shall not be healed by them. What several ways have been prescribed for this, to have sin mortified, is known. The greatest part of popish religion, of that which looks most like religion in their profession, consists in mistaken ways and means of mortification. This is the pretence of their rough garments, whereby they deceive. Their vows, orders, fastings, penances, are all built on this ground; they are all for the mortifying of sin. Their preachings, sermons, and books of devotion, they look all this way….
…This, I say, is the substance and glory of their religion; but what with their labouring to mortify dead creatures, ignorant of the nature and end of the work,—what with the poison they mixed with it, in their persuasion of its merit, yea, supererogation (as they style their unnecessary merit, with a proud, barbarous title),—their glory is their shame…
– John Owen –
from The Mortification of Sin in Believers, volume 6 of Works, pages 16-17