We are bombarded with requests for money. Our bills have to be paid, the mortgage comes every month, our children's schools constantly want us to either buy or sell something, our alma maters want alumni gifts, and even our radio stations have pledge drives. We buy popcorn for boy scouts and cookies for girl scouts and donate an extra dollar at the checkout line in the grocery store; we treat our friends to lunch and give money for homeless and hungry strangers on the street. On top of all of that, we give to churches and charities.
Most of us live very generous lives, and after we've dealt with the non-negotiables like bills and mortgage, we are interested in using our gifts for God's work. Our challenge isn't wanting to give money to good causes; our challenge is knowing which causes are good. We need a filter to determine where our hard-earned money would be most effective for Christ. We don't want to squander what we have on organizations with ineffective management, or unrealistic goals, or a lack of vision. This desire is both appropriate and admirable.
But there are two places that we are challenged in our thinking about generosity.
Keeping Faith In-Between Times: Bring in the Full Tithe
The idea of the tithe appears in throughout the Bible. It's the concept that God wants us to give 10% of our income to Him. We get the first commandment to tithe in Leviticus 27:30-33.
"A tithe of everything from the land, whether grain from the soil or fruit from the trees, belongs to the LORD; it is holy to the LORD. Whoever would redeem any of their tithe must a a fifth of the value to it. Every tithe of the herd and flock - every tenth animal that passes under the shepherd's rod - will be holy to the LORD. No one may pick out the good from the bad or make any substitution. If anyone does make a substitution, both the animal and its substitute become holy and cannot be redeemed."
In Numbers 18:20-24, God gives the tithes to the Levities and priests, so they can accomplish the work of God. But there are two additional implications of the tithe that are helpful.
First, the passage in Leviticus above says that the tithe is "holy to the LORD." In other words, it belongs to God. This is a shift in how we think about our generosity. The first 10% of earnings in the Old Testament did not really belong to the Israelites. That wasn't income that they could distribute as they chose; it was God's money BEFORE they gave it to him. (See Malachi 3:8-12, where God describes keeping the tithe as stealing from Him). This is why the Israelites had "tithes and additional offerings." The additional offerings were from the 90% that belonged to them, and could be distributed as they saw fit. This 90% could be used to feed the family or to feed the poor, to build a house or to build the house of God. But the 10% wasn't their money to give. It was already God's money, and a sign and reminder to the Israelites that all they had came from God as a gift.
Second, the tithe is often connected to the idea of "first fruits," the first produce of a harvest. The Israelites were encouraged to bring their first fruits to God; in other words, to give to God first, and their other concerns second. Those "other concerns" included things like bills, mortgage, school, etc. While we tend to reverse this trend, and give to God whatever is left after the non-negotiables, Jesus would have learned that giving to God was the first and most important non-negoitable in his financial life.
Extras:
There is considerable debate about the tithe in the Old Testament. While the vast majority of references match with the Numbers 18 reading above in concluding that the tithe goes to the Temple and the priests/Levities, there are several passages in Deuteronomy that describe something different.
Deuteronomy 12:5-28 describes another use of the tithe - for a great annual celebratory meal in Jerusalem. And Deuteronomy 26:12-15 describes a third use of the tithe, where 10% of all income is stored up over a 3 year period, and then distributed to the "Levite, the foreigner, the orphan and the widow."
Because of these passages in Deuteronomy, some believe that the celebratory meal in Deuteronomy was only a portion of the tithe, eaten as worship, before the rest was given to the Temple. There are others who believe that the Israelites actually gave 23.3% of their income annually, instead of 10%!