Leviticus 27:11 - Joseph Benson’s Commentary on the Old and New Testaments

Unclean Either for the kind or for the quality of it; if it were such a one as might not be offered. In the case of any unclean beast; that is, which was not allowed to be offered in sacrifice, such as a horse, camel, &c., it was to be valued by the priest, and then the owner had liberty to leave the beast at the priest's disposal, or to redeem it by paying the price set upon it, with a fifth part more. This served as a proper check to men's levity and fickleness in making vows and religious resolutions. It put them in mind not to be rash in opening their mouths to God, and made them feel the inconvenience of repenting of their vows.