The sacramental union is distinguished from the other "unions" in theology like the "personal union" of the two natures in Jesus Christ, the "mystical union" of Christ and his Church, and the "natural union" in the human person of body and soul. It is seen as similar to the personal union in the analogue of the uniting of the two perfect natures in the person of Jesus Christ in which both natures remain distinct: the integrity of the bread and wine remain though united with the body and the blood of Christ. In the sacramental union the consecrated bread is united with the body of Christ and the consecrated wine is united with the blood of Christ by virtue of Christ's original institution with the result that anyone eating and drinking these "elements"—the consecrated bread and wine—really eats and drinks the physical body and blood of Christ as well. Lutherans maintain that what they believe to be the biblical doctrine of the manducatio indignorum supports this doctrine as well as any other doctrine affirming the Real Presence. The manducatio indignorum is the contention that even unbelievers eating and drinking in the Eucharist really eat and drink the body and blood of Christ. This view was put forward by Martin Luther in his 1528 Confession Concerning Christ's Supper: It is asserted in the Wittenberg Concord of 1536 and in the Formula of Concord. The Formula of Concord couples the term with the circumlocution used among Lutherans to further define their view:
Lutherans believe that the words spoken by Jesus Christ at his Last Supper, the Words of Institution, bring about the sacramental union then and at all times whenever the Christian eucharist is celebrated according to his mandate and institution.
Distinction from other doctrines of the Real Presence
This view is sometimes erroneously identified as consubstantiation in that it asserts the simultaneous presence of four essences in the Eucharist: the consecrated bread, the body of Christ, the consecrated wine, and the blood of Christ; but it differs in that it does not assert a "local" presence of the body and blood in the sacramental bread and wine respectively, which is rejected as "gross, carnal, and Capernaitic" in the Formula of Concord. The term "consubstantiation" has been associated with such a "local" inclusion of the Body and Blood of Christ in the sacramental bread and wine as has the term "impanation." Lutherans have also rejected the designation of their position as consubstantiation because they believe it, like transubstantiation, is a philosophical explanation of the Real Presence, whereas the sacramental union provides a description of the Real Presence. Martin Luther distinguished this doctrine from that of transubstantiation and impanation in this way: The Lutheran doctrine of the sacramental union is also distinct from the Reformed view. The Calvinistic view of Christ's presence in the Lord's Supper is that Christ is truly present at the meal, though not substantially and particularly joined to the elements. This is in line with their general belief that "the finite cannot contain the infinite". Lutherans, on the other hand, describe the Personal Union of the two natures in Christ as sharing their predicates or attributes more fully. The doctrine of the sacramental union is more consistent with this type of Christology. The Lutheran scholastics described the Reformed christological position which leads to this doctrine as the extra calvinisticum, or "Calvinistic outside," because the Logos is thought to be outside or beyond the body of Christ.
