Westminster Confession of Faith, Chapter 29
I. Our Lord Jesus, in the night wherein he was betrayed, instituted the sacrament of his body and blood, called the Lord's Supper, to be observed in his church unto the end of the world, for the perpetual remembrance of the sacrifice of himself in his death, the sealing all benefits thereof unto true believers, their spiritual nourishment and growth in him, their further engagement in and to all duties which they owe unto him, and to be a bond and pledge of their communion with him, and with each other, as members of his mystical body.
II. In this sacrament Christ is not offered up to his Father, nor any real sacrifice made at all for remission of sins of the quick or dead; but only a commemoration of that one offering up of himself, by himself, upon the cross, once for all, and a spiritual oblation of all possible praise unto God for the same...
III. The Lord Jesus hath, in this ordinance, appointed his ministers to declare his word of institution to the people, to pray, and bless the elements of bread and wine, and thereby to set them apart from a common to an holy use; and to take and break the bread, to take the cup, and (they communicating also themselves) to give both to the communicants; but to none who are not then present in the congregation.
V. The outward elements in this sacrament, duly set apart to the uses ordained by Christ, have such relation to him crucified, as that truly, yet sacramentally only, they are sometimes called by the name of the things they represent, to wit, the body and blood of Christ; albeit, in substance and nature, they still remain truly and only bread and wine, as they were before.
VII. 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.
VIII Although ignorant and wicked men receive the outward elements in this sacrament, yet they receive not the thing signified thereby; but by their unworthy coming thereunto are guilty of the body and blood of the Lord, to their own damnation. Wherefore all ignorant and ungodly persons, as they are unfit to enjoy communion with him, so are they unworthy of the Lord's table, and cannot, without great sin against Christ, while they remain such, partake of these holy mysteries, or be admitted thereunto.