Martin Luther’s commentary on Matthew 5:13:
For if I cling to this, that Christ alone is my righteousness and holiness, no monk will ever persuade or mislead me by his hood, rosary, this or that work and childish human notion. For through faith I am a judge of all imaginable conditions and ways of living, so that I can condemn everything that offers to show me anything else that is to avail before God. But if I neglect this, and let the treasure go, and am instructed to seek elsewhere and otherwise to be pious, to conciliate God and atone for sin, then I am already prepared for all sorts of snares and nets of the devil , and to let myself be led as he pleases; then presently comes some one who preaches to me: If you want to be pious and serve God, then put on a hood, pray daily so many rosaries, burn so many little candles to St. Anna: then I fall in with this like a blind man and everybody’s fool and prisoner, and do everything I am told, so completely that I cannot defend myself from even the most trifling mistake. See, Christ has himself here foretold this, and given warning that so it would be; and no one has ever lived who knew just how to be on his guard against it. And if we are not now wide awake, and do not take good care that we firmly hold this article, then it will happen to us also, that we hold no article properly and purely, nor cease to err and create factious parties until it is all over, and no preaching or teaching will be of use any more, but we shall stay swine and kine; as it is, alas! already among the great mass, because of our despising the gospel and being grateful for it.
(Luther, Martin (2012-03-12). Martin Luther: Commentary On The Sermon On The Mount (Kindle Locations 1279-1290). . Kindle Edition.) — * also downloadable for a pittance here. *