The moral law (to begin first with it) is contained under two heads, one of which simply commands us to worship God with pure faith and piety; the other, to embrace men with sincere affection. Accordingly, it is the true and eternal rule of righteousness, prescribed for men of all nations and times, who wish to conform their lives to God’s will. For it is his eternal and unchangeable will that he himself indeed be worshiped by us all, and that we love one another.
The ceremonial law was the tutelage of the Jews, with which it seemed good to the Lord to train this people, as it were, in their childhood, until the fullness of time should come [Gal. 4:3–4; cf. ch. 3:23–24], in order that he might fully manifest his wisdom to the nations, and show the truth of those things which then were foreshadowed in figures.
The judicial law, given to them for civil government, imparted certain formulas of equity and justice, by which they might live together blamelessly and peaceably.
Those ceremonial practices indeed properly belonged to the doctrine of piety, inasmuch as they kept the church of the Jews in service and reverence to God, and yet could be distinguished from piety itself. In like manner, the form of their judicial laws, although it had no other intent than how best to preserve that very love which is enjoined by God’s eternal law, had something distinct from that precept of love. Therefore, as ceremonial laws could be abrogated while piety remained safe and unharmed, so too, when these judicial laws were taken away, the perpetual duties and precepts of love could still remain.
But if this is true, surely every nation is left free to make such laws as it foresees to be profitable for itself. Yet these must be in conformity to that perpetual rule of love, so that they indeed vary in form but have the same purpose. For I do not think that those barbarous and savage laws such as gave honor to thieves, permitted promiscuous intercourse, and others both more filthy and more absurd, are to be regarded as laws. For they are abhorrent not only to all justice, but also to all humanity and gentleness.
John Calvin, Institutes of the Christian Religion trans. Ford Lewis Battles, The Library of Christian Classics (Louisville, KY: Westminster John Knox Press, 2011), 4.20.15.