This verse sits inside Folly's banquet, Proverbs 9:13–18. **A character is speaking here. These are Folly's words, not the book's counsel.**
Quick answer
This is the sales pitch, quoted so you can hear it. Folly is speaking, and the very next verse is the narrator correcting her.
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 gives Folly her one line, and it is uncomfortably well written. She does not argue that what she offers is good; she argues that it is stolen and secret, and offers those two facts as the attraction. That is an accurate piece of observation about a real appetite, which is why the line lands. Set against verse 5 it also completes the chapter's menu comparison: Wisdom offered bread and wine she had prepared, and this offer is bread and water whose entire appeal is that they belong to someone else and no one is watching. Nothing is claimed about the taste. The sweetness is in the theft.
What it does not mean
This is not the book's endorsement, and it is not Proverbs observing something bittersweet about forbidden pleasure. It is dialogue. Folly is a character in a two-panel picture, she is making a pitch, and the narrator answers her in the very next sentence by naming who else is at that table. The verse is quoted so often on its own that the attribution has to be stated plainly: read without verse 18, it says the opposite of what the chapter is saying. The book has done this before, giving a seductive speech room to be persuasive in chapter 7 precisely so a reader would recognize it later, and the technique only works if the reader knows who is talking.
Related: Proverbs 9:5 · Proverbs 20:17 · Proverbs 30:20
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.