Jeremiah 17:9 says, “The heart is deceitful above all things, and desperately corrupt; who can understand it?”

This passage is used (and distorted) by many Protestants in a way similar to their frequent citation of Isaiah 64:6 — “all our righteousnesses are as filthy rags.” It’s thought that this proves that no good works are meritorious, that “faith alone” is the way to salvation (which works have nothing to do with), and that sanctification is a separate “optional” category that has nothing to do with salvation, either (which ties in with extrinsic, external, imputed justification). Jeremiah 17:9, like Isaiah 64:6, is interpreted with little or no consideration for context, or of Jeremiah’s overall thought about salvation.

The Protestant idea is that people can do absolutely nothing to be saved and this is because (using these two passages) the heart is utterly “deceitful” and wicked and every righteous act we do is like a filthy rag. Accordingly, the Good News Bible paraphrased Isaiah 64:6 in a spectacularly biased and incorrect way: “Even our best actions are filthy through and through.” That’s pure Protestantism — particularly the extreme Calvinist view of total depravity.

The first thing we need to do is look at the immediate context of Jeremiah 17:9, which would be the very next verse:

I the LORD search the mind and try the heart, to give to every man according to his ways, according to the fruit of his doings.

Three things are apparent from this verse.

First, God is trying the heart of man, looking to see if any given individual has obeyed him or not. If the heart was always desperately wicked, in all people at all times (i.e., if 17:9 is absolutely literal, with no exceptions whatsoever), God’s statement here would make no sense. He wouldn’t have to “try” hearts at all, since all would be equally wicked, just as (not considering his omniscience for a moment) he wouldn’t have to examine all elephants to see whether they had a long trunk or not.

Second, man is not a pawn of his supposedly always evil nature, and so, can decide in his free will whether he will follow God or not, and whether he will allow God to give him the grace to do meritorious good works, in faith — working together with God, as Paul teaches, leading ultimately to salvation. 

Third, it’s clear in this passage that salvation doesn’t come merely from “faith alone” but rather, from the “fruit” of good works (“ways” and “doings”) done in faith, by God’s grace (the latter is taught in Jeremiah 17:5, 7, 14).

Jeremiah makes a clear-cut statement that goes against any notion of no heart whatsoever being capable of good: “You can do good who are accustomed to do evil” (13:23). Can human beings control their hearts and (by extension) their wills, or are they just pawns of the devil? Jeremiah (4:4) teaches that they can choose what their hearts will be like: “Circumcise yourselves to the LORD, remove the foreskin of your hearts” (cf. 9:25-26). Doing so, and getting rid of “evil thoughts” can even “save”: “wash your heart from wickedness, that you may be saved” (4:14). Jeremiah also teaches that we can seek God with all our hearts: “You will call upon me and come and pray to me, and I will hear you. You will seek me and find me; when you seek me with all your heart” (29:12-13).

Jeremiah teaches that God draws all sinners by his grace, without which no one is, or can be saved, and anticipates the New Testament doctrines of justification, faith and the indwelling of the Holy Spirit (indeed, 31:31-34 literally and magnificently foretells of the new covenant in Christ), as well as about God’s mercy and forgiveness (3:12; 15:20-21; 17:5, 7-8, 14; 23:6; 24:7; 31:11; 32:38-40; 33:8; 36:3; 39:18; 42:12). In all of these matters, we essentially agree with our Protestant brothers and sisters. But Jeremiah expresses specifically “Catholic stuff” too. He condemns the extreme antinomian version of “faith alone” (often present in practice, if not in official Protestant doctrine):

Will you steal, murder, commit adultery, swear falsely, burn incense to Ba’al, and go after other gods that you have not known, and then come and stand before me in this house, which is called by my name, and say, `We are delivered!’ — only to go on doing all these abominations? (Jeremiah 7:9-10)

Jeremiah teaches the Catholic doctrine of merit (“your work shall be rewarded” — 31:16), and the New Testament and Catholic doctrine of grace, works and faith all being involved in the process of salvation (see 50 passages from Paul about this).

He also repeatedly emphasizes the biblical and Catholic doctrine of good, meritorious works and obedience to God’s law and moral commands playing a central role in God’s determination of every person’s ultimate salvation or damnation (see 50 passages about that, too):

• “Stand by the roads, and look, and ask for the ancient paths, where the good way is; and walk in it, and find rest for your souls. But they said, ‘We will not walk in it.’” (6:16; cf. 5:23, 28-29);
• “they have not given heed to my words; and as for my law, they have rejected it” (6:19; cf. 7:23);
• “they have rejected the word of the LORD” (8:9; cf. 8:10-12)”;
• “they have forsaken my law which I set before them, and have not obeyed my voice, or walked in accord with it” (9:13; cf. 9:14-16);
• “Hear the words of this covenant and do them” 11:6; cf. 11:7-8; 13:10; 15:6); 
• “Return, every one from his evil way, and amend your ways and your doings” (18:11);
• “I will punish you according to the fruit of your doings, says the LORD” (21:14; cf. 22:3-5, 15-16; 23:6-17; 25:8-9);
• “amend your ways and your doings, and obey the voice of the LORD your God” (26:13; cf. 32:23; 34:17; 38:20; 40:3; 42:11-16, 21-22; 44:23).