The Sacraments: Baptism & the Lord's Supper
In his magisterial work entitled Institutes of the Christian Religion (1559), John Calvin defines a sacrament as "a testimony of divine grace toward us, confirmed by an outward sign, with mutual attestation of our piety toward him." (Inst. IV; xiv; i) In other words, in the administration – by a lawful minister of the gospel – of the signs of water, bread, and wine, God's covenant promises are sealed to our consciences and confirmed in our hearts when received by faith. Indeed, the sacraments of baptism and the Lord's Supper are God's visible words of love, ordained by God to direct our faith toward Christ, the One in whom all of God's promises are gloriously fulfilled.
The Lord's Supper
When we receive the signs of bread and the wine by faith, in a mysterious manner we also receive the thing signified, namely, Jesus Christ and His benefits. After all, "the cup of blessing that we bless, is it not a participation in the blood of Christ? The bread that we break, is it not a participation in the body of Christ?" (I Corinthians 10:16) If this were not true, and we did not receive Christ in the Supper, the Lord's Table would hardly be a means of grace.