“The sin of Judah is written with an iron stylus, engraved with a diamond point on the tablets of their hearts and on the horns of their altars.
The Prophet teaches us here in other words what we have often already seen, — that the Jews in vain sought refuges, for their sin had so much accumulated that it was very apparent. It indeed often happens, that men fall; but God, who is ever inclined to mercy, forgives them; and they are also often led astray through levity, and thus their sins are not engraven on their hearts.
The people had asked (Jer 16:10), What is our iniquity, and what is our sin? as if they could not be charged with any thing worth speaking of, for which God should enter into judgment with them; their challenge was answered there, but here we have a further reply to it, in which, I.
Commenting on Jeremiah 17:1-4
The sin of Judah is written with a pen of iron,.... Or an iron tool, such as engravers use in working on hard matter: and with the point of a diamond; such as glaziers use in cutting their glass; though this is not the word used for a diamond in Exo 28:18, this word is elsewhere translated an adamant, Eze 3:9.