One thing I find odd is that when discussing "tithing," we never really quote the Bible's definition for it. Oh, sure, Malachi 3 talks about what those who didn't tithe back then would receive (but I agree with SpiritualMadMan-- Christ became a curse on our behalf so we would not have any), but I did not see anyone define just what the "tithe" is using Scripture. The word "tithe" just means "tenth" and used alone in that sense does not refer to any type of giving-- you might as well just say "decimal point" or "ten's place."
If you go back in the Law of Moses, you will see that the tithing which is listed DOES NOT...can I say it again? DOES NOT...refer to giving money. It was always giving one tenth from the produce of the land; crops, herds, etc. It was never income. It wasn't even seafood-- a fisherman did not have to give 1/10 of his fish catch to the Levites, nor did the laborer have to give 1/10 of his earnings. Only a land-owner or a herdsman were under this stipulation, because they had received their blessing from the land which was promised (Which simultaneously answers the question as to why Jesus said the Pharisees should tithe FROM THEIR HERBS. Not with money).
Tithing is not almsgiving, and you will never find a biblical definition saying so. The only time money came into the picture was when you could not bring your tithe (a head of cattle or several bushels of crops) to "where God had ordained," then you could sell your tithe-- you could not sell money-- and that the gold or silver from selling your tithe, go to the place where God designated (eventually, was Jerusalem at the Temple), buy whatever you want (meat, wine, etc), and then consume it before the LORD.
As for the 'firstfruits' thing, look it up and you will see it was a one-time offering. When you first bought a field, the first fruits belonged to God. That was it. And remembering that money does not grow on trees, it was produce and vegetation, not cold hard cash.
Why did Jesus, under the Law, not pay tithes from His money (He was a carpenter at one point, after all)? Why did Peter, James, John, or Andrew not tithe from their paycheck? Because it's not biblical.
And then we go back to Abraham, who "tithed" to Melchizedek. One thing to point out is that this was not a religious thing; it was a dispensing of stuff that Abraham did not want. Abraham was not a nomadic warrior chief; He did not engage in tribal warfare very often; He did not even keep the other 90% of the spoils. The other 90% went to the king of Soddom. So Abraham did not "tithe from his increase"; in his mind, it was never his to begin with. And since Abraham nor anyone else did this before or after in the whole of Scripture, it is hardly the foundation on which to base the fundamental teaching that "tithing" is said to be.
But what is it we are to do? GIVE. "Freely you have received and freely shall you give." There was no statistical system of giving in the early church; they simply met needs as they were encountered. Of course, the deacons (sadly, not what "deacon" often is today) were set up in order to better fascilitate this giving. Now, just because "tithing" is effective does not mean that it is correct. If one thinks they are tithing from their paycheck and give to God from their heart, then that is known in the NT as "generousity," not "tithing." God blesses GENEROUSITY. And I submit that a truly generous believer is blessed with more fulfillment, peace, joy, and happiness than the most faithful "tither."
Blessings,
SpyHunter