The guests invited to the Lord's Supper

'He gate it to the disciples, and said, Take, eat.' The sacrament is children's bread. If a man makes a feast, he calls his friends. Christ calls his disciples; if he had any piece better than another, he carves it to them. 

'There is no room for more shades' (Horace). [a shade was a guest not invited by the host but brought by some other guest of importance as one of his party, aka-- a "+1" in our slang]

'This is my body which is given for you' (Luke 22:19). That is, for you 'pistoi', believers. (πιστοι) Christ gave his body and blood to the disciples chiefly under this notion, as they were believers. As Christ poured out his prayers (John 17), so his blood, only for believers; see how near to Christ's heart all believers lie! Christ's body was broken on the cross, and his blood shed for them. 'The election has obtained it' (Rom. 11:7). Christ has passed by others, and died intentionally for them [believers]. 

Impenitent sinners have no benefit by Christ's death, unless a short reprieve. Christ is given to the wicked in wrath. He is 'a rock of offence' (I Pet. 2:8). The blood of Christ is like chemical drops of oil, which recover some patients, but kill others. Judas sucked death from the Tree of Life. God can turn stones into bread, and a sinner can turn bread into stones; the Bread of Life into the stone of stumbling.
--Watson, Thomas. 15 (The Lord's Supper)