Numbers 18:26

26 “Speak to the Levites and say to them: ‘When you receive from the Israelites the tithe I give you as your inheritance, you must present a tenth of that tithe as the LORD’s offering.

Read Numbers 18:26 Using Other Translations

Thus speak unto the Levites, and say unto them, When ye take of the children of Israel the tithes which I have given you from them for your inheritance, then ye shall offer up an heave offering of it for the LORD, even a tenth part of the tithe.
"Moreover, you shall speak and say to the Levites, 'When you take from the people of Israel the tithe that I have given you from them for your inheritance, then you shall present a contribution from it to the LORD, a tithe of the tithe.
“Give these instructions to the Levites: When you receive from the people of Israel the tithes I have assigned as your allotment, give a tenth of the tithes you receive—a tithe of the tithe—to the LORD as a sacred offering.

What does Numbers 18:26 mean?

John Gill's Exposition of the Bible
Numbers 18:26

Thus speak unto the Levites, and say unto them
Aaron was to tell them what a provision would be made for them on account of their service, but Moses was to inform them what part Aaron was to have out of it:

when ye take of the children of Israel the tithes which I have given
you from them for your inheritance;
which was done at the time of their harvest, and of the ingathering of the fruits of the earth:

then ye shall offer up an heave offering of it for the Lord;
in token of gratitude for the liberal provision he had made for the maintenance of them:

[even] a tenth [part] of the tithe;
a tenth part out of the tenth of the produce of the land of Israel.

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