it comes from the bible, a direct quote. It is a Christian principle. I can't tell you the exact quote however
Well, not exactly. The tradition of the tithe predates christianity. The biblical explanation: When the people of Isreal were divided in "houses", one of those "houses" was the Levites, who were designated to be the priests of Isreal. All the other houses were instructed to give 10% of their annual production to the Levites for their support. There are other refrences to particular biblical characters giving 10% of their possessions as thanks or offerings, but the specific idea of the tithe comes from Moses directions to the houses of Isreal.
Our modern christian church has maintained this biblical injuction to tithe, even though we have cast off nearly all other old testament directions to the Isrealites. I would venture to guess that few christian women sacrifice a small bird at the end of their period, for example. Or, to cite an example more familiar to most of us, follow any of the kosher food laws (which are actually spelled out in the same biblical book as the "tithe").
It is a common misconception that the "tithe" is intended to cover all of one's charitable contributions (from a biblical standpoint). However, there are other rules handed down in the books of Moses that direct the Isrealites to leave food in their fields for the poor, forgive debt at regular intervals and release servants from bondage at regular intervals.
I love my church and find it to be a source of solace and spiritual exploration. We do not give 10% of our earnings to the church-- they get more like 1%. The overwhelming majority of the money my church spends is to maintain the church and the staff. Our staff isn't overpaid, but we have three full time ministers, two secretaries, a business manager, a member care minister, a youth minister and two full time caretakers. Our buildings are beautiful and expensive to maintain. Although we mean well, Only a tiny fraction of what the church raises goes to minister to the poor, sick and oppressed. So, I tend to think of the money I give directly to the church as something similar to....."club dues"...that is, money that goes to support services that are meaningful to me and my family.
The money that we give to The Coalition for the Homeless, Habitat for Humanity, etc, is the money that I think of as being truly charitable. And, they get significantly more than the church.