John Calvin Commentary Leviticus 20:25

"Ye shall therefore make a distinction between the clean beast and the unclean, and between the unclean fowl and the clean: and ye shall not make your souls abominable by beast, or by bird, or by anything wherewith the ground teemeth, which I have separated from you as unclean." — Leviticus 20:25 (ASV)

You shall therefore put difference. I have no doubt that this sentence depends on the end of the preceding verse. For although that verse contains a reason to deter them from incest (about which he had been speaking), it also refers to the doctrine before us and serves as a preface to it.

In short, it connects two things, for God here briefly declares His will, not only concerning unlawful and improper intercourse, but also concerning why He forbids His people to eat unclean animals.

Therefore He says, I am the Lord your God, which have separated you from other people. From this it follows that they were prohibited from eating those animals for no other reason than that they might learn from this to take more diligent heed and to withdraw themselves far from all the pollutions of the Gentiles.

He had previously recommended purity through various symbols, and now extends it even to the animals themselves. This reason must be carefully noted: that the distinction between foods is set before them so that they may cultivate purity.

For what is said here would be somewhat meaningless if we did not know that this prohibition was imposed with this objective: that they should not mix indiscriminately with the Gentiles.

Therefore, it is repeated again that they were set apart to be God’s inheritance; and from this it is inferred that holiness was to be cultivated by them, so that they might conform themselves to the example of their God.

Now, it cannot be doubted that the distinction of foods which is prescribed is a supplement to the First Commandment, in which the rule for worshipping God properly and purely is established; and thus religion is protected from all mixtures of superstition.