John Calvin Commentary Exodus 13:8

"And thou shalt tell thy son in that day, saying, It is because of that which Jehovah did for me when I came forth out of Egypt." — Exodus 13:8 (ASV)

And you shall show your son in that day. He repeats what we have already remarked, namely, an injunction for parents to teach their children, so that they may thus transmit the service of God to their descendants. In the preceding chapter it was said, when your children shall say to you, etc.; and now he more briefly commands that God’s goodness should be proclaimed, even if no one should ask about it, because parents ought to be voluntarily inclined to educate their children in the fear of God.

He also repeats, as we have seen above, that the memory of their deliverance should be annually renewed, so that it does not ever fade away. Since religion is easily neglected unless people are diligently engaged in its study, he uses a comparison when he says, it shall be for a sign to you upon your hand, and for a memorial between your eyes. This is as if it had been said that their redemption should be set before their eyes in the Passover, just as the ring that is on the finger, or the ornament that is bound upon the forehead, are constantly seen.

For this purpose also, he had previously desired that the precepts of the Law should be inscribed on the head, on the hands, and on the fringes of their garments. The essence is that in the Passover a monument of God’s grace should exist, so that it might never sink into oblivion, just as ornaments that appear on the forehead and on the fingers awaken attention by being constantly seen.

However, if anyone should rather be of the opinion that Moses alludes to those who, conscious of their own unfaithfulness, devise ways to assist their memory,³²³ I offer them no opposition. It is as if he had said that, since they were prone to forgetfulness, they should use this remedy to awaken themselves to gratitude. He will soon repeat the same injunction in connection with the offering of the firstborn.

The following words, that the Lord’s Law may be in your mouth, confirm the opinion that the Passover has reference to the First Commandment. They intimate that it is not enough to perform the external rite unless it is associated with its proper object, namely, that they should devote themselves to God and to His doctrine.

He mentions the mouth, not because the main thing is to speak or talk about the Law—for if piety lay in the tongue, hypocrites would be the best worshippers of God—but he expressly requires that when each one has privately applied himself to the study of the Law, they should also mutually teach and exhort each other.

³²³ “Et pourtant font des neuds a leurs ceintures, ou quelque marque a leur bonnet;” and therefore make knots in their girdles, or some mark in their cap. — Fr.