The secular make fun of those who tithe like they are just throwing away their money. Of course, if you look at the way people spend money, you could probably find clear ways that people waste dollars. Statistics show that churches on the whole save society loads of cash. But I digress before I ever begin. I mean to give the best argument for tithing. Does God expect us to tithe? Tithing for certain is Old Testament: Abraham tithed pre-Mosaic law (Gen. 14:20), the Mosaic law required it (Lev. 27:32; Num. 18:24; Dt. 12:6; etc.), and God said the one who did not tithe was robbing Him (Malachi 3:8-10). Some argue it is only Old Testament. Not so. First, Christ said He did not come to destroy the law but to fulfill it (Matthew 5:17). Grace is not antinomian (lawless). The law is good (Rom. 7:12). It has its purpose of pointing out transgression. As such, it is a schoolmaster to bring us to Christ by faith (Gal. 3:24, 25).
Anways, the argument. I'm not going to make you turn to 1 Corinthians 9, but that's where it is. Consider these verses there (that means read them):
6 Or I only and Barnabas, have not we power to forbear working? 7 Who goeth a warfare any time at his own charges? who planteth a vineyard, and eateth not of the fruit thereof? or who feedeth a flock, and eateth not of the milk of the flock? 8 Say I these things as a man? or saith not the law the same also? 9 For it is written in the law of Moses, Thou shalt not muzzle the mouth of the ox that treadeth out the corn. Doth God take care for oxen? 10 Or saith he it altogether for our sakes? For our sakes, no doubt, this is written: that he that ploweth should plow in hope; and that he that thresheth in hope should be partaker of his hope. 11 If we have sown unto you spiritual things, is it a great thing if we shall reap your carnal things? 12 If others be partakers of this power over you, are not we rather? Nevertheless we have not used this power; but suffer all things, lest we should hinder the gospel of Christ. 13 Do ye not know that they which minister about holy things live of the things of the temple? and they which wait at the altar are partakers with the altar? 14 Even so hath the Lord ordained that they which preach the gospel should live of the gospel.
Paul argues that he has the right to be materially compensated for his ministry. He gives a number of different arguments for this, including going back into the OT law to make it (vv. 8-10). Obviously Paul thought that the law still applied. In v. 13 he contends that the Levites ("they which minister about holy things") lived "of the things of the temple." The "things of the temple" were the tithes of the congregation of Israel. Now look at v. 14 to get the brunt of this in the words "even so." You should understand "even so" as "just like." The Lord has ordained that the people that preach the gospel should live of the gospel, just like the Levites lived of their particular ministry. The Levites were supported by tithes and so today churches should support their ministers with their tithes.
Many more verses tie into, accentuate, and support this argument. However, this is the best explanation for why tithing is New Testament and ought to be done today. To not do so is essentially then to violate all the New Testament principles and commands on giving. The priority of worship will show up in the pocket book, for where your treasure is, there will your heart be also.