Union with Christ in the Epistle to Diognetus, Ambrose, and Luther
This article will examine statements made in the Epistle to Diognetus, St. Ambrose, and Martin Luther on the question of how a believer’s union with Christ is related to justification. All three of these sources, I assert, ground justification on the basis of a kind of union with Christ. Their formulations differ somewhat, but they all offer us helpful ways of understanding how being united to Christ is a necessary ground of our being justified before God.
Before we look at the statements of our three sources, we must make a clear distinction between the formal union and the mystical union of Christ and the believer and how each of these types of union is related to justification. The former is the basis and source of our justification, while the latter is the result of justification. The former is a legal union that provides the basis of imputation, or God crediting Christ’s righteousness to us, whereas the latter is a spiritual and ontological union which renovates the heart and leads to a new way of life.
This distinction has its roots in Scripture. St. Paul frequently asserts that believers are “in Christ,” and although he does not explicitly say that there is a formal and mystical union, we can see the distinction between these two kinds of union expressed in his letters. A couple of representative passages will help to illustrate this. The apostle says to the Corinthians, “for as in Adam all die, even so in Christ all shall be made alive” (1 Cor. 15:22, NKJV). this verse refers primarily to the formal union, not the mystical union. This is seen in the contrast that is made between being in Adam and being in Christ. It would be difficult to try and maintain that this text is speaking about being “in Adam” in the mystical sense, which would require that we personally and spiritually dwell in Adam and he in us as a result of our unbelief. It is much better to understand this being “in Adam” as Adam being our formal head and representative. For this reason, the contrast being made in this passage by Paul between being “in Adam” and being “in Christ” shows that our being in Christ must refer to a formal union between Christ and the believer. Adam is no longer our formal head and representative—Christ is. Since Christ is now our formal head, substitute, and mediator before God, it follows that instead of being condemned by what comes through Adam, which is the guilt of sin which warrants death, we are saved by what comes through Christ, which is the forgiveness of sins, justification, and eternal life. The righteousness of Christ that is imputed to us on the basis of this union remains in Christ but is imputed to us through our faith in his vicarious sacrifice.
We also find evidence in Paul for the mystical union or personal indwelling of Christ in the believer. The apostle prays for the Ephesians, “that He [the Father] would grant you, according to the riches of His glory, to be strengthened with might through His Spirit in the inner man, that Christ may dwell in your hearts through faith” (Eph. 3:16-17). Here, Paul is clearly speaking about the “inner man” and the strengthening thereof. This has to do with our personal spiritual being. Our inner man is strengthened by the Spirit who dwells in us, and Christ dwells in our hearts by faith as well. In this union, the personal indwelling of Christ in the hearts of believers presupposes that they have already been justified. Having been justified, they receive the strengthening of the Spirit and the personal presence of Christ within their hearts, and thus come to be “filled with all the fullness of God” (Eph. 3:19).
Being filled with all the fullness of God through the strengthening of the Spirit and the indwelling of Christ makes possible the believer’s increasing conformity to Christ, a process which will be completed when we are glorified. Both types of union thus have as their ultimate goal the culmination of God’s saving work for us and in us. Both types of union also are maintained by God as long as faith is present. The mystical union does not displace the formal union or relegate it to some past moment in the believer’s life, but rather daily builds upon it and brings its benefits to fruition. It does not even follow the formal union in a temporal sense, but only in the sense that it exists on the basis of it. Now that the distinction between the formal union and the mystical union has been recognized and delineated, we can see what our three chosen writers say about union with Christ and its relationship to justification.
The Epistle to Diognetus contains within it some of the strongest soteriological language that can be found among all the second-century apologetical literature. Unfortunately, we do not know who authored the letter, but it was obviously someone with profound theological insight. What follows are the most relevant words on the topic of union with Christ written by this ancient Christian:
For what else but His righteousness would have covered our sins? In whom was it possible for us lawless and ungodly men to have been justified, save only in the Son of God? O the sweet exchange, O the inscrutable creation, O the unexpected benefits; that the iniquity of many should be concealed in One Righteous Man, and the righteousness of One should justify many that are iniquitous![i]
The author is clear that it is through a kind of union between Christ and the believer that the believer is justified, especially in his words, “in whom was it possible for us lawless and ungodly men to have been justified, save only in the Son of God?” As to the kind of union this is, if we may assume there is a reciprocal relationship between our sins being “concealed” in Christ and Christ’s righteousness justifying us—and I would argue the writer intends to affirm such a relationship—then one must doubt that the writer is claiming that Christ became ontologically united to iniquity in the concealment of our sins in him. In other words, it seems clear that the author is not claiming that Christ actually became a sinner himself. This is relevant because if there is a true parallel between our sins being concealed in Christ and Christ’s righteousness justifying us, and if our sins are not ontologically united to Christ, then, conversely, Christ’s righteousness must not be ontologically united to us either. The evidence thus suggests that the ancient writer is speaking about a formal union between Christ and the justified sinner. Christ’s righteousness justifies us, not by being imparted to us or made to dwell in us personally, but because the Lord imputes this righteousness to us and counts us as righteous on account of Christ being our representative.
St. Ambrose, the mentor of St. Augustine, speaks much on what it means to be united to Christ and what results from such a wonderful union. Ambrose begins one of his letters with these memorable words: “as far as we are able, let us give our attention to that which is beautiful, comely, and good; let us be occupied with it, let us hold it in mind, so that by its glow and light our souls may become lovely and our minds transparent.”[ii] Ambrose tells us what is the beautiful, the comely, and the good a bit further into the letter. Speaking of Christ, his words are as follows:
He is our peace, He is our Highest Good, for He is the Good from Good, and from a good tree is gathered good fruit. Then, too, His Spirit is good, that Spirit which receives the servants of God from Him and brings them into the right way. Let no one who has the Spirit of God in him deny that He [Christ] is good, since He says of Himself: ‘Is thy eye evil because I am good?’ May there come into our soul, into our innermost heart, this Good which the kind God gives to those who ask Him. He is our Treasure; He is our Way; He is our Wisdom, our Righteousness, our Shepherd and the Good Shepherd; He is our Life. See the number of good things in the one Good![iii]
Ambrose makes two very noteworthy statements in this short letter. First, Ambrose desires that Christ would “come into our soul, into our innermost heart.” This desire to be personally and spiritually united to God and to Christ, so that God in Christ would personally dwell in our hearts and souls, fills the piety of the early church, and Ambrose is no exception. Ambrose is clearly affirming that there is a true mystical union between Christ and the believer.
There is also evidence that the great church father locates our righteousness in Christ alone. Though Christ does truly dwell in us, it is in Christ that our righteousness is found, not in us. The conclusion of the words cited suggest this: “see the number of good things in the one Good!” The righteousness of Christ is not stated to be something in us, something that has been infused, but is instead only found “in the one Good,” who is Christ. The righteousness of Christ that we have access to is not properly ours but his alone. Although Ambrose, like other church fathers, does not distinguish between the formal and mystical unions, it is not difficult to find both being affirmed in his writings.
The teaching that believers are united to Christ is present in Luther as well. In Luther’s Explanations of the Ninety-five Theses, specifically thesis 37, Luther affirms that it is the righteousness of Christ that justifies us, but the reason why the Christian’s righteousness is the righteousness of Christ is because the Christian is made one with him. Luther’s words are as follows:
Therefore, since the spirit of Christ dwells within Christians, by means of which brothers become co-heirs, one body, and citizens of Christ, how is it possible for us not to be participants in all the benefits of Christ? Christ himself has all that belongs to him from the same Spirit. So it happens through the inestimable riches of the mercies of God the Father, that a Christian can be glorified with Christ and can with confidence claim all things in Christ. Righteousness, strength, patience, humility, even all the merits of Christ are his through the unity of the Spirit by faith in him. All his sins are no longer his; but through that same unity with Christ everything is swallowed up in him. And this is the confidence that Christians have and our real joy of conscience, that by means of faith our sins become no longer ours but Christ’s upon whom God placed the sins of all of us. He took upon himself our sins. Christ himself is “the Lamb of God who takes away the sins of the world.” All the righteousness of Christ becomes ours. He places his hand upon us and all is well with us. He spreads his cloak and covers us, blessed Savior throughout all ages, Amen.[iv]
Luther locates the basis of our being “participants in all the benefits of Christ” in our becoming “co-heirs, one body, and citizens of Christ.” The Christian is now able to claim the righteousness of Christ as his own righteousness before God because the Christian is able to lay claim to Christ himself as his own, and so all that is Christ’s now rightfully belongs to the one who is united to him by faith. Luther makes this point even more strongly in his famous sermon “Two Kinds of Righteousness,” where he says the following, “through faith in Christ, therefore, Christ’s righteousness becomes our righteousness and all that he has becomes ours; rather, he himself becomes ours. . . . He who trusts in Christ exists in Christ; he is one with Christ, having the same righteousness as he.”[v] The Reformer affirms that it is the righteousness of Christ that justifies us, and also insists that the way the sinner possesses the righteousness of Christ as his own righteousness is through the possession of Christ himself. In these statements of Luther, we do not find a clear line established between the formal and mystical union of Christ and the believer, yet once again both forms of union are present. Luther beautifully grounds the righteousness that the believer has before God, not in us, but entirely in Christ. That point must not be missed when reading Luther on union with Christ and justification.
In conclusion, the assurance the believer has through being united to Christ is infinite. Much has been made above of the distinction between the two kinds of union the believer has with Christ, but stepping back a bit and seeing both kinds of union together as a whole can encourage us greatly. Christ, in whom alone is our righteousness before God, not only makes us just from without, but personally comes and dwells within us. He simultaneously stands before the Father as our head, our representative, our mediator, our Savior, and sits with us in our struggles, our sufferings, and our daily failures and sins. He never ceases being our mediator before God, and he never leaves us personally stranded like sheep without a shepherd. We are declared righteous due solely to what Christ has done for us on our behalf, and we are daily renewed and strengthened as Christ is in us and is leading us toward that celestial city at the end of this often painful and difficult life. One can only repeat those beautiful words of Ambrose discussed earlier, “see the number of good things in the one Good!”
[i] Joseph Lightfoot, ed., The Apostolic Fathers (Grand Rapids, MI: Baker, 1956) 256-257.
[ii] Ambrose, “Letter 79” in Saint Ambrose: Letters 1-91, trans. Mary Melchior Beyenka (Washington D.C.: Catholic University of America Press, 1954) 438.
[iii] Ibid., 439-440.
[iv] Martin Luther, “Explanations of the Ninety-five Theses, 1518” in Luther’s Works, vol. 31, trans. Carl W. Folkemer (Philadelphia: Fortress Press, 1957) 190.
[v] Martin Luther, “Two Kinds of Righteousness, 1519” in Luther’s Works, vol. 31, trans. Lowell J. Satre (Philadelphia: Fortress Press, 1957) 298.
Jordon Staudenheimer is a pre-seminary student at Concordia Saint Paul University. He is studying to become a pastor in the LCMS.