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.
Westminster Confession (29.1)
Calvin held that though the bread and wine remained unchanged (he agreed with Zwingli that the is of "this is my body...my blood" means "represents," not "constitutes"), Christ through the Spirit grants worshippers true fellowship with himself in heaven (Heb 12:22-24) in a way that is glorious and very real, though indescribable. Christ in this sign perceived through the senses sets forth the grace of God in Christ and the blessings of his covenant. They communicate, seal, and confirm possession of those blessings to believers, who by responsively receiving the sacraments give expression to their fatih and allegience. In them God "remembers" his covenant toward us in Christ and does not give us the just wrath we deserve. The Supper is rightly viewed as a means of grace. The efficacy of the sacraments ...resides not in the faith or virture of the minister but in the faithfuness of God. As the preaching of the Word makes the gospel audible, so the sacraments make it visible, and the Holy Spirit stirs up faith by both means.