One aspect of the Lord's Supper that I sometimes fail to emphasize in my preaching and teaching is that even as our sins are taken away by the body and blood of the Lamb of God, we are also taking up and bearing the burdens and the needs of those flesh and blood people with whom we share the Supper. Luther refers to this in the catechism and in his hymnody, but he does so very explicitly in his treatise entitled, "The Blessed Sacrament of the Holy and True Body of Christ, and the Brotherhoods" (1519). Here are a couple of snippets to whet your appetite to read the whole thing, which appears in Luther's Works, Vol. 35, pp. 49-68. A majority of this will be reprinted in the upcoming issue of Gottesdienst. If you are not yet a subscriber, you can take care of that here.
14. To signify this fellowship, God has appointed such signs of this sacrament as in every way serve this purpose and by their very form stimulate and motivate us to this fellowship. For just as the bread is made out of many grains ground and mixed together, and out of the bodies of many grains there comes the body of one bread, in which each grain loses its form and body and takes upon itself the common body of the bread; and just as the drops of wine, in losing their own form, become the body of one common wine and drink—so it is and should be with us, if we use this sacrament properly. Christ with all saints, by his love, takes upon himself our form [Phil. 2:7], fights with us against sin, death, and all evil. This enkindles in us such love that we take on his form, rely upon his righteousness, life, and blessedness. And through the interchange of his blessings and our misfortunes, we become one loaf, one bread, one body, one drink, and have all things in common. O this is a great sacrament, says St. Paul, that Christ and the church are one flesh and bone. Again through this same love, we are to be changed and to make the infirmities of all other Christians our own; we are to take upon ourselves their form and their necessity, and all the good that is within our power we are to make theirs, that they may profit from it. That is real fellowship, and that is the true significance of this sacrament. In this way we are changed into one another and are made into a community by love. Without love there can be no such change.
15. Christ appointed these two forms of bread and wine, rather than any other, as a further indication of the very union and fellowship which is in this sacrament. For there is no more intimate, deep, and indivisible union than the union of the food with him who is fed. For the food enters into and is assimilated by his very nature, and becomes one substance with the person who is fed. Other unions, achieved by such things as nails, glue, cords, and the like, do not make one indivisible substance of the objects joined together. Thus in the sacrament we too become united with Christ, and are made one body with all the saints, so that Christ cares for us and acts in our behalf. As if he were what we are, he makes whatever concerns us to concern him as well, and even more than it does us. In turn we so care for Christ, as if we were what he is, which indeed we shall finally be—we shall be conformed to his likeness. As St. John says, “We know that when he shall be revealed we shall be like him” [I John 3:2]. So deep and complete is the fellowship of Christ and all the saints with us. Thus our sins assail him, while his righteousness protects us. For the union makes all things common, until at last Christ completely destroys sin in us and makes us like himself, at the Last Day. Likewise by the same love we are to be united with our neighbors, we in them and they in us.
(and this preceding paragraph)
13. There are those, indeed, who would gladly share in the profits but not in the costs. That is, they like to hear that in this sacrament the help, fellowship, and support of all the saints are promised and given to them. But they are unwilling in their turn to belong also to this fellowship. They will not help the poor, put up with sinners, care for the sorrowing, suffer with the suffering, intercede for others, defend the truth, and at the risk of [their own] life, property, and honor seek the betterment of the church and of all Christians. They are unwilling because they fear the world. They do not want to have to suffer disfavor, harm, shame, or death, although it is God’s will that they be thus driven—for the sake of the truth and of their neighbors—to desire the great grace and strength of this sacrament. They are self-seeking persons, whom this sacrament does not benefit. Just as we could not put up with a citizen who wanted to be helped, protected, and made free by the community, and yet in his turn would do nothing for it nor serve it. No, we on our part must make the evil of others our own, if we desire Christ and his saints to make our evil their own. Then will the fellowship be complete, and justice be done to the sacrament. For the sacrament has no blessing and significance unless love grows daily and so changes a person that he is made one with all others.
Luther, M. (1999, c1960). Vol. 35: Luther's works, vol. 35 : Word and Sacrament I (J. J. Pelikan, H. C. Oswald & H. T. Lehmann, Ed.). Luther's Works (Vol. 35, Page 49-68). Philadelphia: Fortress Press.