Yesterday, I started Martin Jaffee's Torah in the Mouth: Writing and Oral Tradition in Palestinian Judaism, 200 BCE-400 CE (New York: Oxford University Press, 2001). What stood out to me was Mishnah Yadayim 4:3, which Jaffee partially quotes on page 80. So I read the passage in my trusty Danby Mishnah, along with Danby's notes.
The passage asks what tithes Israelites in Ammon and Moab must pay in the seventh year. Rabbi Tarfon says they have to pay the Poorman's Tithe, and Rabbi Eleazar b. Azariah decrees that they pay the Second Tithe. Part of the basis for their decisions is the tithe requirement for Israelites living in Egypt and Babylon, which, like Ammon and Moab, are outside of the land of Israel. According to the passage, the rule that Israelites in Egypt pay Poorman's Tithe in the seventh year is the decree of authoritative people known as the elders, whereas the prophets were responsible for the decree that Israelites in Babylon pay the Second Tithe every seventh year. The new elders voting on the policy for the Israelites in Ammon and Moab decide to go with the previous elders rather than with the prophets: they vote for them to pay the Poorman's Tithe every seventh year. When Rabbi Eliezer (different from Rabbi Eleazar b. Azariah) hears the decision, he weeps for joy, for he has a tradition going back to Moses at Mount Sinai that Israelites in Moab and Ammon should pay Poorman's Tithe every seventh year. The deliberations of the elders actually corresponded with God's revelation on Sinai! This passage is an example of what appears to be Jaffee's thesis: that rabbinic literature initially treated halakah as the work of the sages, but they tried over the years to tie it to God's revelation to Moses at Mount Sinai.
Some background information is in order. The Torah mandates two tithes (technically-speaking) for the children of Israel. The first tithe goes to the Levites (Numbers 18:20ff.): it's their due for the work that they do for God, and it also supports them because they don't have an inheritance of land on which they can grow crops or raise animals. In Deuteronomy 14:22-29, we read about the second tithe. The Israelites are to bring the tithe of their corn, wine, oil, flocks, and herds to the central sanctuary, the place that God will choose. If the central sanctuary is too far, then they can convert that stuff into money and take that instead. At the central sanctuary, they are to use the money or tithe to rejoice before God, as they eat, drink, and be merry. But they are supposed to remember the Levite, who has no inheritance. Every three years, they are to devote all of the second tithe to the poor Levite, the resident alien, the orphan, and the widow, all of whom are economically vulnerable and lack the means for self-support. They pool their tithes into a location within their local gates, and the poor come to it to be satisfied.
According to Leviticus 25:1-7, the Israelites in the Promised Land are to let the land lie fallow every seventh year: they are neither to sow nor prune their vineyard. They cannot reap, but they can still eat the increase (which I don't entirely understand), which is also for their servants and the resident alien, who lacks his own land. The land rest of the seventh year and the Jubilee (also in Leviticus 25) both make an important point: the Promised Land belongs to God, so the Israelites are to obey God's instructions regarding it.
Because the Israelites in the Promised Land do not grow anything in the seventh year, they don't pay tithes during that period of time, since ten per cent of zero is, well, zero. But what about the Israelites who live and farm (or ranch) outside of the Promised Land, in Babylon, Egypt, Ammon, or Moab? For them, the rules are different, for they have to pay some tithe. It may be the second tithe, which the Israelites from those locations would preumably bring to the central sanctuary in Israel (if they indeed made that long journey). Or it could be the Poorman's Tithe, meaning perhaps that they'd have to pay it in years 3, 6, and 7 of the seven year cycle.
I thought this was interesting because of the debates over tithing within Armstrongite and ex-Armstrongite circles. Rabbinic literature is sometimes cited in these debates. I remember reading an article in The Journal by Steven Collins (not Eric Camden from 7th Heaven) that cited the Mishnah to support his point of view, which (I think) was that Israel didn't have to pay three tithes, but only one. Some who believe that tithing is not for today have argued that it related solely to the land of Israel. And so it's interesting to see what the Mishnah actually says: it presumes that there's a second tithe (and thus a first one as well) and a "Poorman's Tithe," and it also holds that Israelites outside of the land of Israel need to tithe in some capacity.
As far as my practice goes, I don't pay a full ten percent, but I try to apply the principle of charitable giving, in some way, shape, or form.