Analogy with practical arts: fixed end, subject, and exact definition of the end as justification
1. For just as in practical — and even in productive — disciplines a certain end is set forth, which is the measure and norm of all the other things considered in them, by which it can be known what belongs to them by right of property and what is more or less ancillary and foreign to them: so also theology has a certain end, about which none of those who in every age have been engaged in this kind of study has ever doubted — namely righteousness before God, which whether you call it before God, or remission of sins, or the inheritance of eternal life, or salvation, or by whatever other name, so long as you understand the thing itself, nothing more concerns this our design.
2. Just as in practical disciplines it is usual to consider the subject set under the end that comes — namely the human being — so the human being under vice is no less necessary in this discipline than the human body and its parts in medicine, and without doubt a hundred thousand times more necessary because of the greatness of the most atrocious spiritual disease of all human beings, plainly hidden beneath reason.
3. Just as in practical disciplines and arts it is supremely necessary that the definition of the end itself, which is the principle of cognition, be constituted most accurately — whence Aristotle carefully warns both about this and about other principles near the end of Nicomachean Ethics book 1 chapter 7 that care must be taken that they be rightly defined, since they have great force for what follows — so in sacred theology the most exact definition of the end, or of justification and eternal life, must be sought from the sacred letters.
Hence almost a thousand times Doctor Luther and other orthodox theologians inculcate in their writings, nearly to nausea, that if the article of justification is lost, the whole Christian doctrine is lost at once; likewise that whoever deny the article of justification at once take CHRIST out of the midst; likewise that when the article of justification is known we walk in clearest light, and when it is unknown in densest darkness; likewise that when this one article is well constituted and known the papacy is overthrown. The reason of these assertions is twofold. First, because the justification of the sinful human being before God is the end for whose sake the whole of sacred Scripture has been disclosed from heaven, and so the aim of our whole theology, which for this end is learned in the schools, taught in the church, and practiced. Second, because if this end is not well constituted and defined, those things cannot be rightly known which have been ordained from heaven for attaining the end and prescribed to us in theology as the speech of the kingdom.
Latin
1. Quemadmodum enim practicis, imo et effectricibus disciplinis finis certus est propositus, qui caeterarum rerum omnium, quae in iisdem considerantur, mensura et norma est, qua cognosci potest, quanam ad eas proprietatis jure pertineant, quae vero sint magis minusve ancillae, ab iis aliena: ita et theologiae certus est finis, de quo nemo eorum, qui omnibus seculis in hoc studiorum genere versati sunt, unquam dubitavit, nimirum justitia coram Deo, quam sive coram Deo, sive remissionem peccatorum, sive haereditatem vitae aeternae, sive salutem, sive quocumque alio nomine appellaveris, modo rem ipsam intelligas, nihil ad hoc institutum nostrum magis interest. 2. Quemadmodum in practicis considerari solet, cujus finis venit, constitutum subjectum, de quo quaeritur, nimirum homo vitio non minus est necessarium in hac disciplina, quam corporis humani et ejus partium in medicina, et absque dubio centies millies magis necessaria ob magnitudinem atrocissimi morbi spiritualis omnium hominum infra rationem plane reconditi. 3. Quemadmodum in practicis disciplinis et artibus summopere necessarium est, ut ipsius finis definitio, quae est principium cognitionis, accuratissime constituatur. Unde et Aristoteles, cum de hoc, tum de aliis principiis, lib. 1. Eth. ad Nicomachum cap. 7. cis finem diligenter monet, opera danda ut recte definiantur, siquidem magnum habent momentum ad ea, quae sequuntur. Ita in sacra theologia finis seu justificationis, vitae aeternae exquisitissima definitio e sacris literis quaerenda est. Hinc fere millies D. Lutherus aliique orthodoxi Theologi in scriptis suis et prope ad nauseam inculcant, amisso justificationis articulo, amissam simul esse totam doctrinam Christianam: itemque quotquot negant articulum justificationis, simul e medio tollere CHRISTUM: item articulo justificationis cognito, in clarissima luce, eodemque ignorato, in densissima nos caligine versari: itemque hoc uno articulo bene constituto et cognito papatum everti. Ratio autem harum assertionum duplex est. Prior, quia justificatio hominis peccatoris coram Deo est finis, cujus gratia universa sacra scriptura divinitus patefacta est, adeoque scopus totius theologiae nostrae, quae ob hunc finem in scholis discitur et docetur in ecclesia, exerceturque. Posterior est, quia non bene constituto definito hoc fine, non recte cognosci possunt ea, quae ad finem consequendum divinitus ordinata nobisque in theologia, ut sermone regni, praescripta sunt.