Firstly, I must state the fact that tithing was never intended for Gentiles (you & I, if you are not Jewish). Secondly, I must also state the fact that tithing was never intended for the Christian, whether they be Jew or Gentile. Now, since that is settled, let us examine the Scriptures.
There are those who argue that tithing is relevant today because it was never part of the Law.
For those who believe tithing pre-dated the Law, the fact that tithing preceded the Law (Gen 14:20 reads Abraham gave a pre-law tithe to Melchizedek) does not mean it is apart from the Law.
Because...
The practice of tithing was eventually codified into the Mosaic Law (see Numbers 18:21, Deuteronomy 14:22-23, Deuteronomy 14:28-29, and Deuteronomy 26:12). Some Christians ignore, or are ignorant of this fact and wrongfully use the example of Abraham's pre-Law tithes to infer a requirement for Christian tithing. However, Abraham also offered pre-Law animal sacrifices. It is evident by Isaac's question ("Where is the lamb for the burnt offering?") in Genesis 22:7 that there were pre-Law animal sacrifices.
That goes to say, Christians who cite Abraham's pre-Law tithe as their basis for Christian tithing must also cite, and abide by, Abraham's pre-Law animal sacrifices in order to remain consistent in their doctrinal approach.
The same could be argued for circumcision, another pre-Law practice of Abraham, and clearly not required of Gentiles. One simply cannot indiscriminately pick and choose which of Abraham's actions are still valid today. One must either embrace all of them or none of them!
In regards to Jesus' instruction to the Pharisees about tithing, Matthew 23:23 (see also Luke 11:42) reads: "Woe to you, teachers of the law and Pharisees, you hypocrites! You give a tenth of your spices—mint, dill and cummin. But you have neglected the more important matters of the law—justice, mercy and faithfulness. You should have practiced the latter, without neglecting the former."
Some Christians offer this as prooftext that since Jesus spoke of tithing, it remains applicable for today. However, Scripture must always be understood in its context. To properly understand Matthew 23:23, one must understand the context to whom Jesus was speaking. He was not speaking to Christians, but instead to non-Christian Jews. Such Jews were obligated to obey the entire Mosaic Law, and thus required to tithe, as Jesus correctly pointed out.
In this Scripture, Jesus used tithing as an example of the Law that these hypocritical Jewish leaders were faithful to keep, while neglecting the underlying principles of the Law. He could have chosen a different example of the Law, such as, "...you faithfully sacrifice the required burnt offerings. But you have neglected the more important matters of the Law..." and the meaning of this passage would have been the same. In any case, His words were never directed toward (or intended for) Christians, whether they be Jew or Gentile.
In regards to financial giving. Scripture is clear that "those who preach the gospel should receive their living from the gospel." if they so desire to embrace that right, in which the Apostle Paul waived. (1 Cor 9:14-15)
Therefore, if we do belong to a church (other than a home church) we are expected to financially support its pastor. The pastor should not be expected to support himself with outside work. In addition, if one's church owns a building, then the members of that local church have an expectation to help maintain that property. What's more, local churches have many other ongoing financial needs (utilities, printing costs, etc.). Para-church ministries might also be considered for one's financial giving. Of course, missions and the needy (Red Cross, for example) should also be considered.
In summary, “You must each decide in your heart how much to give. And don’t give reluctantly or in response to pressure. For God loves a person who gives cheerfully.” (2 Cor 9:7)
