Martin Luther on Hebrews 3:13:
It is rightly called the deceitfulness of sin because it deceives under the appearance of the good. This phrase ‘the deceitfulness of sin’ ought to be understood in a much wider sense, so that the term includes even one’s own righteousness and wisdom. For more than anything else one’s own righteousness and wisdom deceive one and work against faith in Christ, since we love the flesh and the sensations of the flesh and also riches and possessions, but we love nothing more ardently than our own feelings, judgment, purpose, and will, especially when they seem to be good. For the same reason Christ said, when he healed the paralytic at the Pool of Bethesda, that it was impossible for such people to be able to believe: ‘How can you believe who receive glory from one another?’ (John 5:44). Why are they not able to believe? Because the ‘deceitfulness of sin,’ that is, the love of their own righteousness, blinds them and hardens their heart. Yet at the same time they think it a good thing to glory in their own righteousness and be pleased with it, though that indeed is the very worst of all vices, the extreme antithesis of faith. Faith rejoices and glories in the righteousness of God alone, that is, in Christ himself.