Charles Ellicott Commentary Proverbs 26:2

"As the sparrow in her wandering, as the swallow in her flying, So the curse that is causeless alighteth not." — Proverbs 26:2 (ASV)

As the bird by wandering, as the swallow by flying. —Rather, As the bird (any small one, especially the sparrow) is made for wandering, and the swallow for flying (where it pleases), so the curse causeless (i.e., spoken without reason) will not come (reach its destination). The Hebrew reads in the margin “to him,” instead of “not,” in the sense that a causeless curse, though it passes out of sight like a bird in its flight, yet returns “to him” who uttered it—an idea expressed in more than one English proverb. (Isaiah 55:11.)