Below is the promised follow-up, in which Luther sets out the passive righteousness of faith, over against all kinds of righteousness that depend on us. Here, in the regnum Christi or “reign of Christ,” we do not work, but are worked upon. This kind of righteousness will always be incomprehensible to the world, where works reign.

Such righteousness is the only possible consolation in trials and afflictions. And, in contradistinction to what is often maintained, putting one’s confidence in it is, far from being the easy way out, the most difficult thing of all. Thus we must be constantly exercised in learning to believe that this really is how God works.

Ultra et supra has omnes est fidei seu Christiana iustitia quae diligentissime discernenda est ab illis superioribus. Sunt enim superiores huic prorsus contrariae, tum quod fluunt ex legibus Caesarum, traditionibus papae et praeceptis dei, tum quod versantur in nostris operibus et a nobis fieri possunt sive ex puris naturalibus (ut sophistae loquuntur) sive etiam ex dono dei (sunt enim et hae iustitiae operum dona dei, ut omnia nostra). Ista autem excellentissima iustitia, nempe fidei, quam deus per Christum nobis absque operibus imputat, nec est politica nec ceremonialis nec legis divinae iustitia nec versatur in nostris operibus, sed est plane diversa, hoc est mere passiva iustitia (sicut illae superiores activae). Ibi enim nihil operamur aut reddimus deo, sed tantum recipimus et patimur alium operantem in nobis, scilicet deum. Ideo libet illam fidei seu Christianam iustitiam appellare passivam. Haecque est iustitia in mysterio abscondita quam mundus non intelligit, imo Christiani non satis eam tenent et difficulter in tentationibus apprehendunt. Ideo semper est inculcanda et assiduo usu exercenda. Et qui eam in afflictionibus et terroribus conscientiae non tenet aut apprehendit, non potest consistere. Nulla enim alia tam est firma ac certa consolatio conscientiarum quam illa passiva iustitia.

Martin Luther, Commentarius in Epistolam ad Galatas, Argumentum (WA 40.1, 40-1)

Beyond and above all these [kinds of righteousness] is the righteousness of faith or Christian righteousness, which we must distinguish most carefully from the foregoing types.^[1] For the foregoing are absolutely contrary to this kind, both because they flow from the laws of the Caesars, the traditions of the pope, and the commandments of God,^[2] and because they turn on our own works and can be done by us,^[3] whether due to pure nature^[4] (as the sophists say) or even due to the gift of God^[5] (for these kinds of righteousness that belongs to works, too, are gifts of God, as is everything that belongs to us).

This kind of righteousness, moreover, is most excellent–namely, the righteousness of faith, which God imputes to us through Christ apart from works. And it is not political, nor is it ceremonial, nor is it the righteousness of the law of God, nor does it turn on our own works; but it is clearly different, that is, it is a purely passive righteousness (just as the foregoing are active).

For there,^[6] we work nothing, nor do we render anything to God, but we only receive and passively experience another working in us, namely, God. For that reason, it is pleasing to call the righteousness of faith or Christian righteousness passive.

And this is the righteousness hidden in a mystery, which the world does not understand. Even Christians do not sufficiently maintain it, and with difficulty do they grasp it in temptations. For that reason, we must always be stuffed full of it and trained in it by continuous application. And he who does not maintain or grasp it in afflictions and the terrors of conscience cannot stand fast. For there is no other consolation of consciences so firm and certain as that passive righteousness.

The translation is my own.