Calvin wrote in his treatise on the Lord’s Supper,
Let us come to the . . . right use, which consists in observing the institution of the Lord with reverence. For whoever approaches this holy sacrament with contempt or indifference, not caring much about following where our Lord calls him, perversely misuses it and thus contaminates it. . . .
If we wish, then, to communicate worthily in the sacred Supper of our Lord, we must hold in firm and hearty confidence the Lord Jesus Christ as our sole righteousness, life and salvation, receiving and accepting the promises which are given us by Him as certain and assured; renouncing on the other hand all other confidence, in order that, distrusting ourselves and all other creatures, we may rest fully in Him and content ourselves with his grace alone. (in John Calvin: Writings on Pastoral Piety [Classics of Western Spirituality; New York: Paulist Press, 2001], 107-108).