Numbers 18:9
This shall be thine of the most holy things, reserved from the fire: every oblation of theirs, every meat offering of theirs, and every sin offering of theirs, and every trespass offering of theirs, which they shall render unto me, shall be most holy for thee and for thy sons.
The verse assigns to Aaron and his sons what is most holy and reserved from the fire, namely every oblation rendered to God, every grain offering, every sin offering, and every trespass or guilt offering, given to them as most holy food to eat. The grain offerings and the sin and guilt offerings brought to the Lord were thus set apart from the portions consumed on the altar fire for the priestly family.
The title most holy stands in the superlative degree, while the seventh-day Sabbath is called holy in the positive degree, yet this does not make the offerings more holy than the Sabbath because the two are never compared with each other. God has only one Sabbath, which He blessed and sanctified and commanded to be kept holy, so it is not one among many that could exceed one another in holiness and does not take the superlative form, yet it is to be regarded as much more holy than the various things called most holy.
Beyond the grain, sin, and guilt offerings named in the verse, the surrounding verses add other offerings and first produce to the priests' allotted provisions. Those reserved portions belong to the priestly family on condition that its members remain fit to partake of them. The verse is part of God's provision for the support of His ministers under the Levitical priesthood, in which the tribe of Levi was set apart from the other tribes for the service of the tabernacle, the Lord gave the tithes of Israel to the Levites to inherit with each member of the other tribes paying a tenth into the treasury, and the Levites were to have no inheritance in the land among Israel, for the tithe is the Lord's and is holy unto the Lord.
The verse shows that the tithe is reserved by the Lord from all the increase placed in man's hands and set apart for a sacred use, while the remaining nine tenths are left at man's disposal under God's government. It designates the tithe as a heave offering belonging to the service of the altar, so sacred that it was to be handled only by the priests, with death as the warning for others who touched it. The instruction in Numbers 18:7-11 that the most holy offerings including grain, sin, and guilt offerings were reserved from the fire for Aaron and his sons is the basis for saying that unauthorized handling of the tithe brought the death penalty. The verse belongs to a chapter that is profitable for people who challenge God's appointed order in pursuit of priestly authority.