This represents nice prose by Martin Luther on the Mirifica Commutatio ‘Wonderful Exchange’:
By this mystery, as the Apostle teaches, Christ and the soul become one flesh. And if they are one flesh and there is between them a true marriage—indeed, the most perfect of all marriages, since human marriages are but poor examples of this one true marriage—it follows that everything they have they hold in common, the good as well as the evil. Accordingly the believing soul can boast of and glory in whatever Christ has as though it were its own, and whatever the soul has Christ claims as his own. Let us compare these and we shall see the inestimable benefits. Christ is full of grace, life, and salvation. The soul is full of sins, death, and damnation. Now let faith come between them and sins, death, and damnation will be Christ’s, while grace, life, and salvation will be the soul’s; for if Christ is a bridegroom, he must take upon himself the things which are his bride’s and bestow upon her the things that are his. If he gives her his body and very self, how shall he not give her all that is his? And if he takes the body of the bride, how shall he not take all that is hers? [Martin Luther, LW 31:351, cited by Carl Trueman in, Justification in Perspective: Chapter 4, Simul peccator et justus: Martin Luther and Justification, 79]
What is significant about this kind of framing is that it magnifies the Pauline, triune, relational frame of salvation. This runs contrary to framing salvation in purely forensic-juridical forms as Melanchthon (Luther’s under-study) is known for. Trueman tries to argue that Luther and Melanchthon were one and the same in their views here, just a difference in language and emphasis. In other words, Trueman would have us believe that Luther affirmed the forensic frame for understanding salvation; even though Luther has statements like the above running through the majority of his corpus. You will have to read this chapter by Trueman to see how he seeks to “Legalize” Luther. Nevertheless, this marriage-framework in Luther runs fluid with Calvin’s unio mystica; both in the mirifica commutatio tradition. Both run counter against the post-Reformed orthodox (Calvinist or even later Lutheran) understanding of salvation as purely juridical or forensic in trajectory.
I find Luther’s statement above to be a beautiful, scriptural, trinitarian, Pauline, Johannine articulation of what salvation entails. Another implication of this, is that salvation is understood to all be grounded in Christ (justification, sanctification, and glorification); and so we no longer have this rupture placed between the objective side of salvation (justification), and the subjective (sanctification), it is all placed and shaped by Christ himself. So Luther offers a participationist understanding of salvation. Which is commendable, and for my money, should be accepted as the best way to understand a framework for thinking of salvation through.