This verse closes Folly's banquet, Proverbs 9:13–18, and closes Collection I. The NKJV's "hell" here translates Sheol.
Quick answer
The narrator answers Folly by naming the other guests. The man accepting the invitation cannot see who is already at the table.
Read the whole unit
The chapter's second table, and the second woman. Everything about her is arranged to mirror the first, and the mirroring is the argument.
Wisdom built a house; this woman already has one and sits at its door. Wisdom hewed pillars, slaughtered, mixed, and set a table; this woman prepares nothing at all. Wisdom sent servants out into the city; this woman sits on a seat. Wisdom called from the highest places of the city; so does she, from the same phrase. And her invitation in verse 16 is, in Hebrew, word for word the same sentence Wisdom spoke in verse 4, addressed to the same two people, the simple and the one lacking heart.
Then the two offers diverge, and the difference is not what anyone would predict. Wisdom offered bread and wine she had made. This woman offers water and bread that are stolen and eaten in secret. Same two categories, and the entire appeal has moved from the food to its provenance. Nothing is claimed about the taste except that being illicit is what makes it sweet.
Two things must be said about how these verses are read.
Verse 17 is a character speaking, and the catalog flags it every time. "Stolen water is sweet, and bread eaten in secret is pleasant" is not the book's counsel and not an endorsement. It is Folly's sales line, quoted so the reader can hear it, and verse 18 immediately supplies the narrator's correction. Lifted out of the chapter, it has been quoted as though Proverbs were observing something wistful about forbidden pleasure. Proverbs is doing the opposite: it is showing you the pitch, and then showing you the guest list.
This is not a chapter about women, and its own design forecloses that. Two women are set against each other here, and the one the book wants you to follow is a woman. The figure who builds, provides, sends, and gives is female, and so is the figure who takes. Anyone reading chapters 5 through 9 as a warning about women has to explain why this book's own embodiment of the good life keeps a house and sets a table. Both figures are personifications, and the contest is between two ways of living, not between a man and a danger.
What this verse contributes
This verse supplies the correction the previous verse required, and it works by turning on a light. Everything Folly said was about the food; the narrator says nothing about the food and instead describes the room. The phrase "he does not know" is the same note chapter 7 ended on, where a young man walked into a snare not knowing it would cost his life, and it is the last thing Collection I says about folly: not that it is stupid, but that it is uninformed. The dinner guests in this house have been there a while.
Why translations differ
"Hell" renders Sheol, and the NKJV's own footnote supplies the alternative. Sheol in the Old Testament is the realm of the dead, where everyone goes, rather than the developed later doctrine of final punishment. The verse describes a house whose guests are already among the dead, which is an image of a road ending early and badly, not a map of the afterlife. It should not be pressed into one in either direction.
From this side of the cross
Collection I ends with two tables and no third option, and that is where a wisdom book has to leave it. What the gospel adds is not a softer contrast but a different host. Wisdom sent her servants into the city; Jesus told of a master who sent his servant into the streets and lanes for the poor and the maimed and the lame and the blind, and then further out to the highways and hedges until the house was full (Luke 14:21–23). The invitation in this chapter goes to whoever is simple. The one in that story goes to whoever is left, and it is still going out.
Related: Luke 14:21–23 · Proverbs 7:23 · Proverbs 2:18–19 · Proverbs 5:5
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.