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Since the question was edited to specify Baptist teachings, here's a quick note that should provide the shortest answer...
Baptists encourage tithing, but do not require it. More frequently, they equate "stewardship" with obedience, and their definition of stewardship includes cheerful and sacrificial giving, which "goes beyond the tithe" to also include acts of service.
My Original (Verbose) Answer:
Malachi 3:8 states that God himself views disobedience to tithe as stealing. This is because God has show us that we are to contribute to our teachers, and by commanding it he has laid claim on that portion of our income. By keeping resources that God has allocated for a different purpose, we are stealing it from him as long as we still have it.
Many doctrines adhere to a strong belief that every good thing we have comes from God (James 1:17)- so by that logic, this isn't really an unfair command. The unfair thing would be if a parent gives a kid two snacks, and says one is for sharing with his schoolteacher... but the kid kept both to themselves.
You could also think of it like failing to pay your taxes... the government takes that really seriously, and can even charge you with criminal tax evasion.
Also, this article is really good.
Upvote:4
Tithing [or more generally "giving"] is as noted in another reply "encouraged" by most Baptists. It is interesting that in some of the earliest Baptist confessions tithe is not mentioned as an ordinance. In fact any reference to money in regards to the church is incidental:
The 1644 London Confession, http://www.reformedreader.org/ccc/h.htm Article 38:
That the due maintenance of the officers aforesaid, should be the free and voluntary communication of the Church, that according to Christ's ordinance, > they that preach the Gospel, should live on the Gospel and not by constraint to be compelled from the people by a forced law.
and The 1646 http://www.reformedreader.org/ccc/1646lbc.htm :
The ministers of Christ ought to have whatsoever they shall need, supplied freely by the church, that according to Christ's ordinance they that preach the Gospel should live of the gospel by the law of Christ. 1 Cor. 9:7,14; Gal. 6:8; Phil. 4:15,16; 2 Cor. 10:4; 1 Tim. 1:2; Ps. 110:3.
More recent Baptist declarations seem to have no clear statement of tithe, but do speak of due stewardship.
Southern Baptist 2000 Faith and Message XIII:
Stewardship God is the source of all blessings, temporal and spiritual; all that we have and are we owe to Him. Christians have a spiritual debtorship to the whole world, a holy trusteeship in the gospel, and a binding stewardship in their possessions. They are therefore under obligation to serve Him with their time, talents, and material possessions; and should recognize all these as entrusted to them to use for the glory of God and for helping others. According to the Scriptures, Christians should contribute of their means cheerfully, regularly, systematically, proportionately, and liberally for the advancement of the Redeemer's cause on earth.
It seems it is a matter of stewardship, not "tithe." "To give as you have been prospered."