In this passage from the Institutes IV.14.7, Calvin argues that the rejection of Christ in the sacraments does not imply that the sacraments are not efficacious. Instead, to those who receive them in faith, the sacraments are evidences of God's grace to us, "seals of the good-will which he entertains toward us." They "nourish, confirm, and increase our faith."
The Sacraments: An Offer Of Mercy And A Pledge Of His Grace--Calvin
It is irrational to contend that sacraments are not manifestations of divine grace toward us, because they are held forth to the ungodly also, who, however, so far from experiencing God to be more propitious to them, only incur greater condemnation. By the same reasoning, the gospel will be no manifestation of the grace of God, because it is spurned by many who hear it; nor will Christ himself be a manifestation of grace, because of the many by whom he was seen and known, very few received him. ... It is certain, therefore, that the Lord offers us his mercy, and a pledge of his grace, both in his sacred word and in the sacraments; but it is not apprehended save by those who receive the word and sacraments with firm faith: in like manner as Christ, though offered and held forth for salvation to all, is not, however, acknowledged and received by all. Augustine, when intending to intimate this, said that the efficacy of the word is produced in the sacrament, not because it is spoken, but because it is believed. Hence Paul, addressing believers, includes communion with Christ, in the sacraments, as when he says, "As many of you as have been baptized into Christ have put on Christ" (Gal. 3:27). Again, "For by one Spirit we are all baptized into one body" (1 Cor. 12:13). But when he speaks of a preposterous use of the sacraments, he attributes nothing more to them than to frigid, empty figures; thereby intimating, that however the ungodly and hypocrites may, by their perverseness, either suppress, or obscure, or impede the effect of divine grace in the sacraments, that does not prevent them, where and whenever God is so pleased, from giving a true evidence of communion with Christ, or prevent them from exhibiting, and the Spirit of God from performing, the very thing which they promise. We conclude, therefore, that the sacraments are truly termed evidences of divine grace, and, as it were, seals of the good-will which he entertains toward us. They, by sealing it to us, sustain, nourish, confirm, and increase our faith.