Matthew Henry Commentary Proverbs 30:15-17

"The horseleach hath two daughters, [crying], Give, give. There are three things that are never satisfied, [Yea], four that say not, Enough: Sheol; and the barren womb; The earth that is not satisfied with water; And the fire that saith not, Enough. The eye that mocketh at his father, And despiseth to obey his mother, The ravens of the valley shall pick it out, And the young eagles shall eat it." — Proverbs 30:15-17 (ASV)

Cruelty and covetousness are two daughters of the horseleech, that still cry, Give, give, and they are continually uneasy within themselves. Four things never are satisfied, to which these devourers are compared. Those who are always coveting are never rich. And many who have come to a bad end have admitted that their wicked ways began by despising their parents' authority.