John Calvin Commentary Jeremiah 17:1

"The sin of Judah is written with a pen of iron, [and] with the point of a diamond: it is graven upon the tablet of their heart, and upon the horns of your altars;" — Jeremiah 17:1 (ASV)

The Prophet teaches us here, in other words, what we have often already seen: that the Jews sought refuges in vain, for their sin had accumulated so much that it was very apparent. Indeed, it often happens that people fall; but God, who is always inclined to mercy, forgives them; and they are also often led astray through frivolity, and thus their sins are not engraved on their hearts.

But Jeremiah says that nothing remained for that nation but to be entirely swept away, because their iniquity was past recovery. If they had been lightly sprinkled with vices, there might still have been a remedy for them; but when their iniquities were engraved on their hearts, on their marrow and bones, what more remained for them? He had said before,

Can the Ethiop change his skin? (Jeremiah 13:23)

Though the Ethiop may change his skin, and also the panther, yet you are still like yourself. They had so completely imbibed a contempt for God, and also perverseness, that they could not by any means be restored to a right mind. We now perceive, then, the meaning of the Prophet in this passage.

He says that the sin of Judah was written with an iron pen, with the point of adamant; as though he had said, “They are not only slightly imbued with iniquity, for then there might be some healing; but iniquity is engraved on their inmost feelings, as though one had engraved it with adamant or with an iron pen.”

Therefore, it appears that they were wholly unworthy of pardon, as they were in no way capable of receiving mercy, however much God might have been inclined to receive them into favor. For their obstinacy had closed the way of salvation; nor could they apply to themselves the promises, for they require repentance in sinners.

He then adds, It is graven on the table of their heart; as though he had said, that they were so addicted to iniquity, that all their inward parts bore the impressions of it. Therefore, it follows that the Jews were so proved to be guilty, that they in vain contrived evasions, for their own conscience condemned them.

At the same time, I consider the Prophet as speaking not only of guilt, but also of sin itself, and of their propensity to evil. He means then that the Jews had not only sinned and transgressed God’s law in an uncommon way, but that they were also so given up to wickedness as to delight in the iniquity that was engraved on their hearts.

He calls, by a metaphor, the affections or feelings "the tables of the heart": for he compares the heart to tables. As writing appears when cut in stone or brass, so when a sinful impression is made on the hearts of people, iniquity itself may be said to be engraved on the tables of the heart.

He afterwards adds, And on the horns of your altars. He had spoken of the heart; he now proceeds further, showing that an evidence of hidden iniquity appeared openly.

If he had spoken only of their hearts, the Jews might have objected and said, “How can you penetrate into our hearts? Are you God, to examine and try our inward emotions?” But the Prophet adds that their iniquity was sufficiently known by their altars.

He at the same time intimates that they alleged the name of religion in vain, for under that pretense they especially sinned against God, because they had vitiated his pure worship. And to confirm this very thing he adds—