Why is the sin of Judah written with a “pen of iron” on the “tablet of their heart” and on “the horns of their altars”?

Jeremiah 17:1–27 appears to have a collection of sayings that do not follow any clear flow of thought or pattern. This has led one commentator to refer to this chapter as Jeremiah’s miscellaneous file.¹ The theme that unifies the chapter is the Lord’s judgment on the ongoing sin of Judah. This is particularly the case for the first passage (Jeremiah 17:1–13) where the important Hebrew word leb or lebab holds the passage together. The word is translated as heart and is frequently used in the Old Testament to refer to the inner life of humans where all thoughts, desires, words, and decisions originate from.² It is therefore the central place from which human worship flows and where sin resides.

Another important aspect that unitesJeremiah 17:1–13 is the speaker. It becomes clear that it is the Lord speaking in Jeremiah 17:1–4. The speaker is less clear in Jeremiah 17:5–13. However,Jeremiah 17:5 starts with the words, Thus says the Lord. Even if Jeremiah is his spokesman, it is the Lord who describes the blessed and cursed man in Jeremiah 17:5–8 in a way that reflects the words of Psalm 1:1–6. It is therefore reasonable to assume that the Lord continues to speak the proverbial sayings in Jeremiah 17:9–13. This entire passage (Jeremiah 17:1–13) is therefore the Lord speaking to and about Judah, either describing the nation's sin directly (Jeremiah 17:1–4) or using proverbs and hymns that the people themselves would have spoken and sung (Jeremiah 17:9–13).³

The first reference to the heart in Jeremiah 17:1–13 is the fact that the sin of Judah is written with a pen of iron, with a point of diamond it is engraved on the tablet of their heart. It becomes clear in Jeremiah 17:3 that it is the Lord who is speaking. He is speaking to Judah, but he uses the third person to address them. This damning statement is for all to hear, not just Judah. The sentence for Judah’s sin is given in the first- and second-person form (Jeremiah 17:3–4). This dramatic shift in person highlights the rhetorical nature of the judgment oracle.⁴

The fact that the Lord says that sin is engraved on the tablet of their heart, draws very deliberate and important links with Mt Sinai. There the Lord had instructed Moses to engrave the Ten Commandments of his covenant law on tablets of stone (Exodus 24:12). But now, says the Lord, instead of faithfulness to the law, deep in the hearts of his covenant people are hearts engraved with sin.⁵ The tool that has been used to engrave sin on their hearts is described as a diamond tipped pen. This refers to a stylus or a chisel made from iron and strong enough to cut into rock (see Job 19:24). The imagery suggests that the sin is permanent, especially in a society that relied on word of mouth where only the most important information was written down to make it permanent.⁶ This image is in stark contrast to the promise of Jeremiah 31:1–40 where the Lord promises to write his law on the hearts of his people (Jeremiah 31:33). Only the Lord himself can deal with sinful human hearts.

Judah’s sin is not only engraved on the tablets of their hearts but also, says the Lord, on the horns of their altars. There are two possible references being made. The first is the altar in the temple which had two stone projections on the top corners. Blood was smeared on these corners when sacrifices were offered as a sign of atonement (Exodus 27:2; Exodus 29:12; Exodus 30:1–3; Leviticus 4:7,Leviticus 4:30,Leviticus 4:34;Leviticus 8:15; Leviticus 16:18). The implication, therefore, is that because of their sinful hearts, Judah’s sacrifices actually represented stubborn ongoing rebellion before the Lord and not atonement. The second possible reference is to the many altars that Judah built to offer sacrifices to false gods; these too had horns on them. These sacrifices were blatant signs of Judah’s stubborn sinfulness. The fact that the Lord refers to altars and not just the altar makes it more likely that he is referring to the altars used in pagan worship.⁷ This is made more likely by the reference to pagan altars in the next verse. Either way, the point is being made that deep in the hearts of the nation is a stubborn rejection of the Lord and a turning to other gods. They certainly do not love the Lord with all their hearts, soul, mind and strength as the covenant demands (Deuteronomy 6:5).