Martin Luther on Psalms 131:3

Verse. 3. Let Israell wait on the Lord [or trust in the Lord] from henceforth and for euer.

This verse sheweth plainly that the Prophet speaketh here of that presumption which is contrary to faith, and is called the presumption of mans owne righteousnes. Therefore he exhorteth the faithfull to trust in the Lord, and withall to abide in humilitie. to mortifie that trust and confidence which man hath in the lawe and in his owne righteousnes. This shall ye doe (saith he) if ye trust in the Lord, not onely for this day or to morrowe, but now and for euer. So that ye muste haue a certaine continuall and a constant presumption (if I may so say) of the mercie of God, of the forgiuenes of sinnes, and of the righteousnes that commeth by Christ. Contrariwise, ye must beware that ye neuer presume of your owne workes: albeit they ought to be holy and according to the law of God. For this naked, and this onely trust ought to remaine, which is called the confidence of the free mercy of God, offered vnto vs in Christ. This trust is sure and neuer deceiueth vs. For God is no lyer, but faithfully performeth that he hath promised. Doe thou therefore but trust, and still faithfully rest vpon his promise, But here we are not without daunger of the deuill, whiche goeth about with all his might and power, to bring vs from this assuraunce and trust of the mercie of God towardes vs in Christ. Wherefore we must fight, and with continuall battaile practise this doctrine against the deuill and spirituall wickednes, which by all meanes goe about, first to lift vs vp with pride and presumption, and afterwards to throwe vs downe againe to desperation.

But God worketh a contrary way. For first he terrifieth vs and casteth vs downe, that afterwards he may raise vs vp againe. He bringeth vs downe to hel, that he may bring vs back againe. The dugge of grace also he sometimes taketh from vs, that we may learne what our owne righteousnes is wont to doe, namely to oppresse vs with desperation. And this he doth to the ende that wee hauing experience thereof, should not followe our owne sense and reason, but raise vp our selues with a sure hope & trust in Christe, whereby the dead are restored to life and saued. This mercie is as a strong heauen or firmament ouer vs, wherwith we beeing couered, are safe and sure where so euer we be. Esa. 25.4. So Esay calleth it a shadow against the heate, because we are couered and defended by the mercie of God, against wrath, desperation, the deuill & death. This shadow who so euer doe forsake, shal suffer intolerable heat. Thus we learne by this verse, that Dauid speaketh of that damnable presumption of our owne righteousnes, & exhorteth vs to fight against it with a sure hope of Gods eternall mercie, and a constant faith. This is the onely way whereby we are saued.