1. “Akin to the preaching of the gospel, we have another help to our faith in the sacraments, in regard to which, it greatly concerns us that some sure doctrine should be delivered, informing us both of the end for which they were instituted, and of their present use.
First, we must attend to what a sacrament is. It seems to me, then, a simple and appropriate definition to say, that it is an external sign, by which the Lord seals on our consciences his promises of good-will toward us, in order to sustain the weakness of our faith, and we in our turn testify our piety towards him, both before himself, and before angels as well as men.
We may also define more briefly by calling it a testimony of the divine favour toward us, confirmed by an external sign, with a corresponding attestation of our faith towards Him.
You may make your choice of these definitions, which in meaning differ not from that of Augustine, which defines a sacrament to be a visible sign of a sacred thing, or a visible form of an invisible grace, but does not contain a better or surer explanation. As its brevity makes it somewhat obscure, and thereby misleads the more illiterate, I wished to remove all doubt, and make the definition fuller by stating it at greater length.”
3. “From the definition which we have given, we perceive that there never is a sacrament without an antecedent promise, the sacrament being added as a kind of appendix, with the view of confirming and sealing the promise, and giving a better attestation, or rather, in a manner, confirming it. In this way God provides first for our ignorance and sluggishness, and, secondly, for our infirmity; and yet, properly speaking, it does not so much confirm his word as establish us in the faith of it.”*
*That is, the sacrament cannot make the promise of God objectively more certain, but it can make our faith in God’s promise subjectively more certain. God’s Word is always absolute, strong, unchangeable, and “settled in heaven”; but our faith, throughout this life is always relative, weak, changeable, and frequently in need of confirmation and assurance. Thus we properly distinguish between the objective certainty of God’s Word, and the subjective certainty of our faith.
-John Calvin, Institutes of the Christian Religion Book 4, Chapter 14, Sections 1 & 3