As miraculous, incredible and wonderful as it sounds, Our Lord Jesus Christ is not content to present Himself to us in only one way (mode). Rather, by the Holy Spirit, we know that He is present to us in at least three ways.
The first way is His physical presence. This occurred when the Holy Spirit overshadowed the Virgin Mary so that she conceived in her womb the Son of God. Our Lord’s second way is His sacramental presence. By the Holy Spirit, Jesus Christ unites Himself (both His divine and human natures) with bread and wine. The third way Our Lord presents Himself to us is His ecclesiastical or churchly presence. This presence also occurs by the Holy Spirit. He unites the faithful together into one communion in Christ’s mystical Body. So two distinct things are combined: Our Lord Jesus and all believers. He is the Head and we are His body.
Just as with His physical and sacrament presence, so also in His ecclesiastical presence Our Lord’s Body is two natures in one Person. For the Church, these two natures are an historical, institutional nature which everyone can see and point to; and a mystical nature which we can see and confess only by the grace of the Holy Spirit. For we are members of His Body—and not of some spiritualized body which no one can see.
The point is that Our Lord presents Himself in outward, manifest ways which men—imbued by the Holy Spirit—can point to and say, “This is the Body of Christ.”
Furthermore, the Lord’s three presences are not separate but interdependent. One could say that they share a perichoretic relationship. His physical presence makes possible His sacramental presence. And His sacramental presence makes possible his churchly presence. For we see Our Lord’s churchly presence most clearly and distinctly at the altar—when the Body of Christ (churchly presence) gathers to feast of the Body of Christ (sacramental presence) which suffered, died and rose for our justification (physical presence).
Yet one parish's particular altar does not exhaust or complete the definition of Our Lord’s churchly presence. If it did, then Jesus would be confined to one place. Or, if He did appear in other churches, then He would be split into many bits all over the world; or He would be duplicated and reproduced. But because of Our Lord’s ascension, the entire Lord Jesus is present sacramentally at every altar. Based on this sacramental miracle, and for the same reason, Our Lord is present not only in one church but across many churches.
Therefore, we ought not simply point at one congregation and say, “This is the Body of Christ.” We also ought to point at a group of congregations—churches in communion fellowship with each other because of Christ’s sacramental presence—and say, “This group of churches, this communion fellowship, this institution is the Body of Christ.”
So Our Lord’s churchly presence is not unlike His physical or sacramental presence. Because Our Lord took flesh, we can and must point to Jesus and say, “This man is God.” Because of Our Lord’s Word and Spirit, we can and must point to the consecrated bread and say, “This bread is Christ’s Body.” In the same way, we can and must point to a communion fellowship that holds to the true faith and say, “This is the Body of Christ—God’s church on earth.”
Condensed and slightly revised from "Addendum III."