“First, we must consider what a sacrament is. It seems to me that a simple and proper definition would be to say that it is an outward sign by which the Lord seals on our consciences the promises of His good will toward us in order to sustain the weakness of our faith; and we in turn attest our piety toward Him in the presence of the Lord and of his angels and before men. Here is another briefer definition: one may call it a testimony of divine grace toward us by an outward sign, with mutual attestation of our piety toward Him.” (Calvin, Inst. IV, xiv, I)
Calvin seeks here to make the sacrament a simple but profound sign in agreement with both God and man, with man being caught-up in both God’s presence & power!