Shared ground
Proverbs 9:18 functions as the narrator’s “reveal” after Folly’s attractive invitation. The text explicitly says the person who accepts her offer “doesn’t know” (know) the real situation. What looks like harmless pleasure is tied to death.
The verse also portrays Folly’s house as already populated: “the dead are there.” And it says her “guests” (those who took her invitation) are in “the depths” (depths) of Sheol (Sheol). Taken together, the plain sense is that Folly’s pathway produces a repeated pattern of destruction, not life.
Where interpretation differs (only where needed)
Two questions commonly arise from the imagery.
One is whether “the dead” and “depths of Sheol” should be read as literal death (an early grave) or as a metaphor for life-ruin so severe it is compared to death.
A second is how concrete “Sheol” is meant to be here: primarily “the grave/the realm of the dead” as a warning about death’s outcome, or a more developed picture of the underworld as a destination.
Why the disagreement exists
Proverbs regularly uses death-language both for actual death and for ruin that feels death-like. Also, “Sheol” can name the grave and the realm of the dead in Israel’s poetic vocabulary, so readers differ on how much the verse is insisting on one versus using vivid warning imagery.
What this passage clearly contributes
This verse makes an explicit contrast between appearance and reality: Folly’s offer hides an end that is deadly. It strengthens a major theme in Proverbs 1–9: choices presented as sweet or secret can still move “downward,” ending in death and Sheol. It also frames Folly’s invitation as part of a larger pattern—her “guests” are many, and their end is described as already sealed.