Shared ground
The passage starts with an observation the speaker says he has seen: moral character and life outcomes do not line up in a simple way. A “righteous” person can “perish” even while living righteously, and a “wicked” person can “live long” while doing evil (v.15). This is presented as a real pattern within the speaker’s “days of vanity,” meaning his fleeting, frustrating experience of life.
From that mismatch, the text gives paired cautions. First, it warns against becoming “overly righteous” and “overly wise” in a way that ends in self-ruin (v.16). Second, it warns against swinging to the opposite extreme—becoming “too wicked” and “foolish,” which can end in an early death (v.17). Verse 18 ties the two cautions together: it is “good” to keep hold of both, with “fearing God” named as the stabilizing orientation.
Where interpretation differs
Some disagreement centers on what “overly righteous” and “overly wise” mean (v.16). One reading takes it as a warning against a performative or self-made righteousness—using morality or wisdom as a tool for control, superiority, or self-protection, which can backfire. Another reading takes it more as a warning against severe, rigid scrupulosity that creates needless harm (to oneself and others), rather than against righteousness itself.
A second point concerns the promise-like line in v.18 (“will come forth from them all”). Some understand it as escaping the traps of both extremes. Others read it more as avoiding the outcomes associated with the extremes (self-ruin and early death), without claiming a guarantee of painless life.
Why the disagreement exists
The key phrases are brief and can be heard in more than one direction. “Overly” can mean “too much” in intensity, or “in the wrong way,” and the text does not spell out a single example. Also, the unit begins by denying a neat reward system (v.15), which makes readers cautious about taking v.18 as a straightforward guarantee.
What this passage clearly contributes
Explicit claims in the text: life can be unfair in visible outcomes (v.15); extreme self-driven righteousness/wisdom can be self-destructive (v.16); extreme wickedness/foolishness can shorten life (v.17); holding both warnings together is “good,” and “fear of God” is presented as the steadying stance (v.18).
Reasonable theological inference: “fearing God” functions here less like a technique to control outcomes and more like a posture that resists both despair-driven compromise and control-driven moral overreach (compare the book’s wider emphasis on limits “under the sun,” Ecclesiastes 1:14).