Calvin:

1) Here, indeed, they disclose their impiety, not only more clearly, but also more grossly. The device of opus operatum is recent, and was coined by illiterate monks, who had never learned anything of the nature of Sacraments. For in Sacraments God alone properly acts; men bring nothing of their own, but approach to receive the grace offered to them. Thus, in Baptism, God, washes us by the blood of his Son, and regenerates us by this Spirit; in the Supper he feeds us with the flesh and blood of Christ. What part of the work can man claim, without blasphemy, while the whole appears to be of grace? The fact of the administration being committed to men, derogates no more from the operation of God than the hand does from the artificer, since God alone acts by them, and does the whole. Calvin, Selected Works, vol, 3, p., 176.

2) Then the Scripture finds occasion for exhortation in all the benefits of God that it lists for us, and in the individual parts of our salvation. Ever since God revealed himself Father to us, we must prove our ungratefulness to him if we did not in turn show ourselves his sons [Malachi 1:6; Ephesians 5:1; 1 John 3:1]. Ever since Christ cleansed us with the washing of his blood, and imparted this cleansing through baptism, it would be unfitting to befoul ourselves with new pollutions [Ephesians 5:26; Hebrews 10:10; 1 Corinthians 6:11; 1 Peter 1:15,19]. Ever since he engrafted us into his body, we must take especial care not to disfigure ourselves, who are his members, with any spot or blemish [Ephesians 5:23-33; 1 Corinthians 6:15; John 15:3-6]. Calvin, Institutes 3.6.3.

3) Washing it with the washing of water. Having mentioned the inward and hidden sanctification, he now adds the outward symbol, by which it is visibly confirmed; as if he had said, that a pledge of that sanctification is held out to us by baptism. Here it is necessary to guard against unsound interpretation, lest the wicked superstition of men, as has frequently happened, change a sacrament into an idol. When Paul says that we are washed by baptism, his meaning is, that God employs it for declaring to us that we are washed, and at the same time performs what it represents. If the truth–or, which is the same thing, the exhibition of the truth–were not connected with baptism, it would be improper to say that baptism is the washing of the soul. At the same time, we must beware of ascribing to the sign, or to the minister, what belongs to God alone. We must not imagine that washing is performed by the minister, or that water cleanses the pollutions of the soul, which nothing but the blood of Christ can accomplish. In short, we must beware of giving any portion of our confidence to the element or to man; for the true and proper use of the sacrament is to lead us directly to Christ, and to place all our dependence upon him. Calvin, Commentary, Ephesians 5:26.

4) Wherefore are we baptized, but to be washed from all our spots, that we may be pure and clean before God, that we may be members of Jesus Christ, that we may be clothed in his righteousness, & (to be short) that we may be renewed by the Holy Ghost? Now, lies it in the mortal man that baptizes us, to give us all these things? No, if we consider him but as a man in his own peculiar person. But sith [since] it is God’s will that the ministers of his word should baptize in his name: baptism must needs have that virtue notwithstanding that it be delivered by the hand of a man. Calvin, Sermons on Deuteronomy, Sermon 16, Deut 3:12-22, p., 93.

5) Again, we see that God is contented with few ceremonies. For it is not his will that we should have any more decking, lights, perfumes, cakes, sacrificings of beasts, nor other such things: but his will is that in our baptism we should have such assurance of our washing and cleansing by the grace that is purchased for us in our Lord Jesus Christ, as should continue with us for ever. Calvin, Sermons on Deuteronomy, Sermon 82, Deut 12:8-14, p., 505.

6) We have at this day the Sacraments. Indeed we have not so great a multitude, as the fathers had, for it were more than we need for us, because we have the substance of all the old shadows our Lord Jesus Christ. But yet for all that, God does still at this day apply himself to our rudeness by his sacraments. In the water of baptism we have a testimony that we be washed and made clean, and that we be renewed by the Holy Spirit. Now then we must not muse upon the water; but when we see the visible sign, we must rise aloft, and understand, that God accomplishes the thing in truth, which is signified unto us by the visible Sacrament. Calvin, Sermons on Deuteronomy, Sermon 174, Deut 30:9-14, p., 1081.