This is a case where little outweighs large. "A little folly" may seem insignificant, but it outweighs things as important as wisdom and honor. The pleasant odor of the carefully-crafted ointment is gone. Darbys translation minces no words: "Dead flies cause the ointment of the apothecary to stink and ferment" (Ecc 10:1).
In the previous 6 verses, Solomon extolls the great value of wisdom (9:13), although the majority may not appreciate its worth (vv 14, 15). Wisdom provides safety, though it may not bring honor (v 15). It transcends strength, though despised and unheeded (v 16). Wisdom generally gains significance, though others may appear more prominent (v 17). It can produce security, though one sinner can undo its benefits (v 18). It likewise promotes success, even though "dead flies" can undo that as well (10:1). The next two verses sum up wisdoms value, which affords skillfulness in every circumstance.
The threat, "one sinner destroyeth much good," is external. The greater threat is internal - a little folly outweighing wisdom and honor. To many, this verse teaches that one act of foolishness can destroy honor gained over many years. As relevant and valuable as that truth is, another possible meaning may be even more searching.
Dead flies dont spoil the perfume by falling into it. Only if they remain in the ointment will they do their corrupting work. Over time, a little folly - not checked, judged, or even noticed - eventually undoes the good of wisdom and honor in the man himself and perhaps even the good others have received through his wisdom. Those stinging (as some linguists suggest), but now dead, flies are like so many of our poisonous, natural tendencies. Traces of pride, stubbornness, lust, temper, deceitfulness, and a swarm of other things, when tolerated within us, do their corrupting work.
An apothecary mixes ingredients to make perfume. "The art of the apothecary" was the model for mixing the holy, anointing oil (Exo 30:25). Could the "perfume" of someone with an ability so used for holy things begin to "stink and ferment"? Could a believer blindly ignore dead flies within until he has spoiled his potential for God and for good?
The holy anointing oil, when poured on a mans head, honored him (e.g. Lev 8:12). The apothecarys ointment anointed the head of an honored guest (Luke 7:46). Could the relationships by which we honor others be destroyed by dead flies within?
If ones head lacked no ointment (Ecc 9:8), this indicated health and abundance (see also Psa 23:5; 45:7). Could we lose our spiritual health and joy because of dead flies?
The articles that follow point to qualities that, like wisdom, are of great value to God, although despised in the world. Let us emulate these and seek grace to remove the dead flies.
"Tis only in Thee hiding
I know my life secure . . ."