The proper application of the pronoun

The gospel is not just a story about Jesus written in a book called “the Bible.” The story needs a proper foundation that Luther called “the proper application of the pronoun” by which Jesus’ story is preached and given “for you.”...Christ’s story must function as law and gospel in your own life. That means that when Luther says “gospel” it includes not only Christ and what he did, but it also includes you as a sinner for whom he did it.

(p.131, Steven Paulson, Luther for Armchair Theologians)

Luther talks about this at length in his Commentary on Galatians 1:4. I apologise for the long quotation in an old translation:

But weigh diligently every word of Paul, and especially mark well this pronoun our; for the effect altogether consisteth in the well applying of the pronouns, which we find very often in the Scriptures, wherein also there is ever some vehemency and power. Thou wilt easily say and believe that Christ the Son of God was given for the sins of Peter, of Paul, and of other saints, whom we account to have been worthy of this grace; but it is a very hard thing, that thou, which judgest thyself unworthy of this grace, shouldest from they heart say and believe, that Christ was given for thine invincible, infinite, and horrible sins. Therefore, generally, and without the pronoun it is an easy matter to magnify and amplify the benefit of Christ, namely, that Christ was given for sins, but for other men’s sins which are worthy. But when it cometh to the putting to of this pronoun our, there our weak nature and reason starteth back, and dare not come nigh to God, nor promises to herself that so great a treasure shall be freely given unto her, and therefore she will not have to do with God, except first she be pure and without sin...

We must use these words of St Paul, in the which he giveth a very good and true definition of Christ in this manner: “Christ is the Son of God, and of the Virgin, delivered, and put to death for our sins.” Here, if the Devil allege any other definition of Christ, say thou, the definition, and the thing defined, are false: therefore I will not receive this definition. I speak not this without cause: for I know what moveth me to be so earnest, that we should learn to define Christ out of the words of Paul. For indeed Christ is no cruel exactor, but a forgiver of the sins of the whole world. Wherefore if thou be a sinner (as indeed we are all) set not Christ down upon the rainbow, as a judge, (for so shalt thou be terrified, and despair of his mercy) but take hold of his true definition, namely, that Christ, the Son of God, and of the Virgin, is a person, not that terrifieth, not that afflicteth, not that condemneth us of sin, not that demandeth an account of us for our life evil passed; but hath given himself for our sins...

Learn this definition diligently, and especially so exercise this pronoun our, that this one syllable being believed, may swallow up all thy sins: that is to say, that thou mayest know assuredly, that Christ hath taken away the sins, not of certain men only, but also of thee, yea, and of the whole world. Then let not thy sins be sins only, but even thy own sins indeed; that is to wit, believe thou that Christ was not only given for other men’s sins, but also for thine.”

(Martin Luther, Commentary on Galatians)