“The third incomparable benefit of faith is that it unites the soul with Christ as a bride is united with her bridegroom. By this mystery, as the Apostle teaches, Christ and the soul become one flesh (Eph. 5:31-32). And if they are one flesh and there is between them a true marriage- indeed the most perfect of all marriages, since 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.
“The third incomparable benefit of faith is that it unites the soul with Christ as a bride is united with her bridegroom.”
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 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…
“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.”
Who then can fully appreciate what this royal marriage means? Who can understand the riches of the glory of this grace? Here this rich and divine bridegroom Christ marries this poor, wicked harlot, redeems her from all her evil, and adorns her with all his goodness. Her sins cannot now destroy her, since they are laid upon Christ and swallowed up by him. And she has that righteousness in Christ, her husband, of which she may boast as of her own and which she can confidently display alongside her sins in the face of death and hell and say, “If I have sinned, yet my Christ, in whom I believe, has not sinned, and all his is mine and all mine is his,” as the bride in the Song of Solomon (2:16) says, “My beloved is mine and I am his.” This is what Paul means when he says in 1 Cor. 15:17, “Thanks be to God, who gives us the victory through our Lord Jesus Christ,” that is, the victory over sin and death, as he also says there, “The sting of death is sin, and the power of sin is the law,” (1 Cor. 15:56).”
Martin Luther, Christian Liberty, pp. 14-15