Jamieson, Fausset and Brown on Ecclesiastes 8:15

15. no better thing, &c.--namely, for the "just" man, whose chief good is religion, not for the worldly.

abide--Hebrew, "adhere"; not for ever, but it is the only sure good to be enjoyed from earthly labors (equivalent to "of his labor the days of his life"). Still, the language resembles the skeptical precept (1Co 15:32), introduced only to be refuted; and "abide" is too strong language, perhaps, for a religious man to apply to "eating" and "mirth."