5. Now, if we choose to investigate whether it is right to administer baptism to infants, shall we not say that a man is talking nonsense or indeed raving who would halt with the mere element of water and outward observance, but cannot bear to turn his mind to the spiritual mystery? If any account of this is made, it will be evident that baptism is properly administered to infants as something owed to them. For in early times the Lord did not deign to have them circumcised without making them participants in all those things which were then signified by circumcision [cf. Gen. 17:12]. Otherwise, he would have mocked his people with mere trickery if he had nursed them on meaningless symbols, which is a dreadful thing even to hear of. For he expressly declares that the circumcision of a tiny infant will be in lieu of a seal to certify the promise of the covenant. But if the covenant still remains firm and steadfast, it applies no less today to the children of Christians than under the Old Testament it pertained to the infants of the Jews. Yet if they are participants in the thing signified, why shall they be debarred from the sign? If they grasp the truth, why shall they be driven away from the figure? Notwithstanding, the outward sign so cleaves to the word in the sacrament that it cannot be separated from it; yet if the sign is considered separately from the word, which, I ask you, shall we esteem more? Obviously, since we see that the sign serves the word, we shall say that it is under the word, and shall relegate it to a lower place. Therefore, since the word “baptism” is applied to infants, why shall the sign, which is an appendix of the word, be denied to them? This one reason, if no others were at hand, would be quite enough to refute all those who would speak in opposition. The objection that there was a stated day for circumcision is sheer evasion. We admit that we are not now bound to certain days like the Jews; but since the Lord, without fixing the day, yet declares that he is pleased to receive infants into his covenant with a solemn rite, what more do we require?

6. Yet Scripture opens to us a still surer knowledge of the truth. Indeed, it is most evident that the covenant which the Lord once made with Abraham [cf. Gen. 17:14] is no less in force today for Christians than it was of old for the Jewish people, and that this word relates no less to Christians than it then related to the Jews. Unless perhaps we think that Christ by his coming lessened or curtailed the grace of the Father—but this is nothing but execrable blasphemy! Accordingly, the children of the Jews also, because they had been made heirs of his covenant and distinguished from the children of the impious, were called a holy seed [Ezra 9:2; Isa. 6:13]. For this same reason, the children of Christians are considered holy; and even though born with only one believing parent, by the apostle’s testimony they differ from the unclean seed of idolators [1 Cor. 7:14]. Now seeing that the Lord, immediately after making the covenant with Abraham, commanded it to be sealed in infants by an outward sacrament [Gen. 17:12], what excuse will Christians give for not testifying and sealing it in their children today?
And let no one object against me that the Lord did not command that his covenant be confirmed by any other symbol than circumcision, which has long since been abolished. There is a ready answer that for the time of the Old Testament he instituted circumcision to confirm his covenant, but that after circumcision was abolished, the same reason for confirming his covenant (which we have in common with the Jews) still holds good. Consequently, we must always diligently consider what is common to both, and what they have apart from us. The covenant is common, and the reason for confirming it is common. Only the manner of confirmation is different—what was circumcision for them was replaced for us by baptism. Otherwise, if the testimony by which the Jews were assured of the salvation of their posterity is taken away from us, Christ’s coming would have the effect of making God’s grace more obscure and less attested for us than it had previously been for the Jews. Now, this cannot be said without grievously slandering Christ, through whom the Father’s infinite goodness was more clearly and liberally poured out upon the earth and declared to men than ever before. And if so, we must admit that at least it should not be concealed with more malign intent, nor revealed with weaker testimony than under the dim shadows of the law.

John Calvin, Institutes of the Christian Religion ed. John T. McNeill, trans. Ford Lewis Battles, The Library of Christian Classics (Louisville, KY: Westminster John Knox Press, 2011), 4.16.5–6.