I think it was Luther who said that a man required two conversions, the first of his heart and the second of his wallet. Have you ever noticed how some people are preeminently quotable, such that all sorts of pithy sayings get attributed to them whether or not they said it? So Luther, or maybe Chesterton, or Churchill, or maybe Oscar Wilde. It fits best with Luther though, so let’s run with that.
I want to begin by summarizing in a paragraph what I understand our obligations with regard to tithing to be, and then to briefly expand on each one of those points.
The tithe is a continuing moral obligation for the people of God (1 Cor. 9:13-14). The lawful recipients of the tithe are those who labor in the ministry (1 Cor. 9:14), the poor (Dt. 14:29), and the merchants who supply the goods for your thanksgiving feasts (Dt. 14:23-29). The tithe is owed on the increase of wealth (Dt. 14:22), not on the wealth itself. The tithe is to be paid on the increase that is brought into your barns, and not on the part of the crop that the locusts ate, which has ramifications for the old net/gross question. And last, the church is to teach authoritatively on the obligation to tithe, but is not to do so in any way that could reasonably be interpreted as a self-serving merchandizing of the gospel (Phil. 4:17).
So let’s work through these. First, there is no dispute that the Levites of the Old Testament were supported by the tithe. They had no inheritance like the other tribes; the Lord was their inheritance. This meant that their needs were supplied by the tithe that the other tribes paid on their increase. Paul says in 1 Cor. 9:14 that ministers of the gospel in the new covenant were to be supported in exactly the same way (even so, just the same way, kai houtos). The tithe predated Moses (Heb. 7:2), and the tithe has survived him.
The tithe is not limited to what goes into the offering at church. A portion of it should go there (Gal. 6:6), of course, but it may also go to your cousin with Wycliffe, the homeless guy at the bus station, Add it all up, and it should come to at least ten percent of your increase.