Leviticus 7:16

Be a vow; offered in performance of a vow, the man having desired some special favour from God, and vowed the sacrifice to God if he would grant it. A voluntary offering, which a malt freely offered to God, in testimony of his faith and love to God, without any particular injunction from God, or design of his own special advantage thereby. See Leviticus 22:23 Ezekiel 46:12. On the morrow also the remainder of it shall be eaten, which was not allowed for the thankoffering; the reason of which difference is to be fetched only from God's good pleasure and will, to which he expects our obedience, though we discern not the reason of his appointments.