The Lord’s Supper as a sacrament signifies the benefits of Christ’s mediation. The bread and wine signify Christ crucified and His benefits (Westminster Confession of Faith 29.5, 7). More specifically, the bread is the sign of Christ’s body, and the wine is the sign of His blood (Matt. 26:26–28; 1 Cor. 10:16). Significantly, these signs are said to be united to the realities they signify. There is “a spiritual relation, or sacramental union, between the sign and the thing signified” (WCF 27.2). Because of this sacramental union, the sign is distinguished from that which it signifies, but it is not separated from it.
The Lord’s Supper is a seal because it confirms the promise of God regarding the reality of the benefits received by those who partake of the Lord’s Supper in faith. Those who partake in faith actually do “feed upon his body and blood” (WLC 168). The Lord’s Supper exhibits the benefits of Christ in the sense that those benefits are truly held forth to believers. This does not mean that the bread and wine have some kind of inherent power. The exhibition of the benefits of Christ depends wholly on the work of the Holy Spirit and the promise of God in the words of institution. But what are the benefits exhibited?
Worthy receivers outwardly partaking of the visible elements in this sacrament, do then also, inwardly by faith, really and indeed, yet not carnally and corporally, but spiritually, receive and feed upon Christ crucified, and all benefits of His death: the body and blood of Christ being then, not corporally or carnally, in, with, or under the bread and wine; yet, as really, but spiritually, present to the faith of believers in that ordinance, as the elements themselves are to their outward senses. (WCF 29.7)
The confession indicates that there is a parallel between what is happening outwardly and visibly and what is happening inwardly and invisibly. Believers really “receive and feed upon Christ crucified,” but not “carnally or corporally.” This happens spiritually because the body and blood of Christ are present to the faith of believers rather than being corporally present “in, with, or under the bread and wine.” This is the vertical aspect of the Lord’s Supper, the sacramental union between the invisible heavenly realities and the visible earthly actions and elements.
As we partake of Christ in the supper, we are spiritually nourished and thus grow in grace. Additionally, as we spiritually partake of the body and blood of Christ, our union with Him is strengthened. The Lord’s Supper is also an occasion to “testify and renew our thankfulness and engagement to God.” We are to remember Christ’s death on the cross for our sins and to thank God for His atoning work on our behalf.
There is also a horizontal aspect to the supper. As Augustine and John Calvin explained, the Lord’s Supper is a “bond of love” among believers. As we partake of the supper, we are to understand that we are all members of the same mystical body of Christ. If all Christians are united to Christ as their one Head, all Christians are united to one another in the one body of Christ. This understanding of our union with Christ and our communion with each other is to result in mutual love and fellowship, all to the glory of Christ (1 Cor. 11:17–34).