A whip for the horse - Correction is as suitable to a fool, as a whip is for a horse, or a bridle for an ass.
SDA Bible Commentary (limited)
Volume 1-7
3. A rod. A whip serves to spur on the horse and the mule and a bridle guides them in the right way and curbs unwise bursts of speed. The fool needs sharp correction if he is to be kept from harming himself and others by unwise actions (see chs.10:13; 19:29).