Commentaries:
Israelites gave tithes to the Levites to perform the work of the Tabernacle and later the Temple. Because they were involved in God's work and had no significant land of their own, the Levites had to be supported by the rest of the congregation of Israel.
Richard T. Ritenbaugh
Tithing
Other Forerunner Commentary entries containing Numbers 18:20:
Leviticus 27:30-33