Knowing the historical background behind the tithing laws will give you a clearer picture of the Biblical tithe.
The first historical point is that the Biblical tithe had to come from within the land of Israel.
The second historical point is that the tithing laws were a part of the Old Covenant, which included blessings for obedience and curses for disobedience.
The third historical point is that the tithing laws required the Tribe of Levi (the Levitical priests and their Levite-assistants).
The Tribe of Levi descended from Levi, one of the twelve sons of Israel. The Tribe of Levi were also called Levites. Moses and his older brother Aaron were Levites. Aaron was the firstborn son in their family.
Since Aaron was the firstborn son in his family, God set him and his sons apart from the rest of the children of Israel to minister as priests (Exodus 28-29). From this point on during the Old Covenant, Aaron and his male descendants were the only ones who were allowed to come near God to serve as priests. Together, the sons of Aaron composed the Levitical priesthood.
What about the Levite-assistants?
In Exodus 32 during the false worship of the golden calf, the Tribe of Levi were the only ones who didn’t participate. When Moses came down the mountain and saw the rebellion, he stood at the entrance to the camp and shouted, “All of you who are on the Lord’s side, come here and join me.” And all the Levites gathered around him” (Exodus 32:25-26). Moses told the Levites that God said to take their swords and kill everyone who committed idolatry by worshiping the golden calf. “The Levites obeyed Moses’ command, and about 3,000 people died that day. Then Moses told the Levites, “Today you have ordained yourselves for the service of the Lord, for you obeyed him even though it meant killing your own sons and brothers. Today you have earned a blessing” (Exodus 32:28-29).
Because they remained faithful to God during the rebellion and obeyed Him when He said to kill the idolaters, the Levites ordained themselves for service unto God. Through this act, they became assistants to the Levitical priests.
So, to recap. . . Aaron and his male descendants became the Levitical priests. And the rest of the male Levites became assistants to the priests. Both the Levitical priests and their Levite-assistants played an integral role in Israel’s tithing system. It isn’t possible to keep the tithing laws without them.