Upvote:1
When the tithe system was set up, the only income that existed for Israelites was agricultural. Wealth was entirely in terms of animals and crops. So in the context when the law was given, the command is to "give a tenth of your agricultural income", but the command is just as much "give a tenth of all your income", since those meant the same thing.
As Israel became more settled and less dependent on agriculture it would have become necessary to decide whether the original command meant "all income" or "just agriculture". Ancient Israel decided that it meant "all income" and Christians follow suit.
It is also worth pointing out that law in Biblical times was "normative" rather than "prescriptive". Whereas we are used to laws being exact definitions, ancient laws were examples to be applied. So if the ancient law said you had to repay someone if their ox fell down your well, that didn't mean you were exempt if their goat or sheep did.
Upvote:2
After the fall harvest, people would travel to Jerusalem for the Feast of Tabernacles. People would reserve a tenth of their harvest for what, in addition to being a religious experience, was like an annual week-long holiday.
For those that lived far from the city, bringing a tenth of their harvest would be impractical, so they sold it locally and instead carried their tithe as cash.
“You shall truly tithe all the increase of your grain that the field produces year by year. And you shall eat before the LORD your God, in the place where He chooses to make His name abide, the tithe of your grain and your new wine and your oil, of the firstborn of your herds and your flocks, that you may learn to fear the LORD your God always. But if the journey is too long for you, so that you are not able to carry the tithe, or if the place where the LORD your God chooses to put His name is too far from you, when the LORD your God has blessed you, then you shall exchange it for money, take the money in your hand, and go to the place which the LORD your God chooses. And you shall spend that money for whatever your heart desires: for oxen or sheep, for wine or similar drink, for whatever your heart desires; you shall eat there before the LORD your God, and you shall rejoice, you and your household. — Deuteronomy 14:22–26