This verse states, in the strongest terms available to it, that declaring a guilty person righteous is detestable to God. The New Testament says God justifies the ungodly. That tension is real, and the entry below does not resolve it by softening either text.
Quick answer
The verse is about a corrupt courtroom: a judge who calls a guilty man innocent, or an innocent man guilty. Both pervert the one institution meant to protect people.
Read both lines
The setting is judicial, and the two halves are the two directions a verdict can be corrupted. Isaiah describes exactly this scene when he condemns those "who justify the wicked for a bribe, and take away justice from the righteous man" (5:23), which is the same pairing in the same order. The chapter itself supplies the motive twice over, at verse 8 with the bribe that looks like a jewel and at verse 23 with the bribe taken under cover. What the verse condemns is not mercy. It is a verdict sold, in which guilt is declared away because someone paid, and the person who was actually wronged is left with nothing.
What it does not mean
This verse is not an argument against forgiving people, and it should never be used to insist that someone must be punished before they can be received. It describes a judge's official verdict in a court, not a person's decision to forgive a wrong done to them, and the same chapter commends covering a transgression as an act of love (17:9). Nor does it teach that God's grace is a legal loophole. Anyone reading it that way has to explain Romans 3:26, where the cost is the entire point.
From this side of the cross
Scripture puts the sharpest form of the problem in God's own mouth: "For I will not justify the wicked" (Exodus 23:7). And then Paul writes that faith is counted as righteousness "to him who does not work but believes on Him who justifies the ungodly" (Romans 4:5). The words are the same words. At the level of what is being described, both sentences name the same act, declaring a guilty party righteous, and it is worth saying plainly that this looks like a collision.
Paul knew it did, and he answered it directly rather than avoiding it. The whole argument of Romans 3 is that God had to be both "just and the justifier of the one who has faith in Jesus" (3:26), and the way He managed both was the cross: Christ set forth as the propitiation, so that God's righteousness is demonstrated in the very act of acquitting the guilty.
That is precisely what the corrupt judge of Proverbs 17:15 does not do. His verdict costs him nothing and costs the guilty nothing; the debt is not paid, it is waived for a fee, and the wronged party absorbs the loss. God's verdict costs Him everything. The guilt is not overlooked, dismissed, or priced at a bribe. It is transferred and paid in full, which is why justification is not a miscarriage of justice but its most expensive satisfaction.
So the proverb and the gospel are not in conflict. The proverb rules out exactly the thing the cross refused to do, which is to call a guilty person righteous cheaply.
Related: Romans 4:5 · Romans 3:24–26 · Exodus 23:7 · Isaiah 5:23 · Proverbs 17:23 · Proverbs 24:24
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.