John Calvin Commentary Numbers 18:31

"And ye shall eat it in every place, ye and your households: for it is your reward in return for your service in the tent of meeting." — Numbers 18:31 (ASV)

And you shall eat it. Because the tithes were considered to be among the sacred offerings, a question might arise whether it was lawful to eat them anywhere except in the sanctuary. God therefore declares that when the Levites had separated the δευυτεροδεκάτας (the second tithes), the residue passed into the nature and condition of ordinary food, since they might then eat in any place of the bread made of grain from the tithe, like the produce of their own fields.

The reason that is added seems by no means appropriate; namely, that it was the reward for the labor which they performed in the service of the tabernacle. For from this it was rather to be inferred that this food was peculiarly destined for the ministers while they were discharging their official duties, and keeping watch in the tabernacle, or killing the victims at the altar.

But since by God’s command they were scattered over the whole land, and did not cease to be ministers of the tabernacle on account of the distance of their residence, it was justly permitted that, wherever they might be, they should eat of the food appointed them by God.

If it were allowable to take the particle כי, ki,²²⁵ adversatively, the sense would be clearer.

In the next verse he confirms the same declaration, that is, that they should be free from all guilt when they had honestly paid the priests.

Yet at the same time they are strictly admonished that they should not commit any fraud. For God declares that it would amount to sacrilege if they should have dishonestly embezzled any of it, and threatens them with capital punishment, because “to pollute the holy things” of the people is equivalent to profaning whatever was consecrated in the name of the whole people.

²²⁵ כיfor, or or because. —— W.