The bread from heaven is the physically manifest flesh of Jesus. That includes all believers in the assembly who are flesh of His flesh and bone of His bone (
Eph 5:30 For we are members of his body, of his flesh, and of his bones.) Eating the bread is a profession that we recognise all who love and follow Jesus as being Christ's body, so that how I treat a Christian is how I am treating Christ, and eating the bread with others confesses that the other communicants are in my heart and I am in their hearts. This is why we need to only take communion if we are treating other Christians as Christ's body. We will be exposing ourselves to discipline by the tormentors who will be allowed to inflict sickness or death if we partake of communion with a spirit that rejects other believers, which is to reject Christ's body while professing to be a member of Christ.