So far as justification is concerned, Christ and I must be so closely attached that He lives in me and I in Him. What a marvelous way of speaking!
Because He lives in me, whatever grace, righteousness, life, peace, and salvation there is in me is all Christ’s; nevertheless, it is mine as well, by the cementing and attachment that are through faith, by which we become as one body in the Spirit.
Since Christ lives in me, grace, righteousness, life, and eternal salvation must be present with Him; and the Law, sin, and death must be absent. Indeed, the Law must be crucified, devoured, and abolished by the Law—and sin by sin, death by death, the devil by the devil.
In this way Paul seeks to withdraw us completely from ourselves, from the Law, and from works, and to transplant us into Christ and faith in Christ, so that in the area of justification we look only at grace, and separate it far from the Law and from works, which belong far away…
But faith must be taught correctly, namely, that by it you are so cemented to Christ that He and you are as one person, which cannot be separated but remains attached to Him forever and declares: ‘I am as Christ.’
And Christ, in turn, says: ‘I am as that sinner who is attached to Me, and I to him. For by faith we are joined together into one flesh and one bone.’
Thus Eph. 5:30 says: ‘We are members of the body of Christ, of His flesh and of His bones,’ in such a way that this faith couples Christ and me more intimately than a husband is coupled to his wife.
Martin Luther, Luther’s Works, Vol. 26: Lectures on Galatians, 1535, Chapters 1-4, ed. Jaroslav Jan Pelikan, Hilton C. Oswald, and Helmut T. Lehmann, vol. 26 (Saint Louis: Concordia Publishing House, 1999), 167–168.