Every so often a google ad shows up on my browser with the statement "tithing is unscriptural."  I once researched this and found a lot of theories, but not much that it is backed up by God's Word.  The truth is tithing (Christians giving 10% of your income to the Church) is still for today.  

There are many Scriptures throughout the Old Testament on tithing.  This principle has been in God's heart from the beginning of humanity, but critics don't argue these verses .. they argue the seeming silence of the New Testament.  

I had my own uncertainty in Bible College.  When we begin to study the Scriptures in depth, it can change many faulty perceptions we have had about our faith.  The truth is, I would tithe whether or not it was a command of Jesus - because it benefits my church and God's Kingdom around the world.  However, I came upon a verse I could't deny:

"You should tithe, yes, but do not neglect the more important things."  - Jesus (Matthew 23:23, NLT)

These are the direct words of Jesus to the Pharisees.  Not only do we have the command of Christ, but also the example of the Church down through the centuries.  I love this article by Christian History and Biography:

"Recently released statistics from the Barna Research Group indicate that ... only 3% of adults contributed 10 percent of their 2002 income to churches, which marks a 62 percent decrease from 2001 when 8 percent of American adults tithed. Among born-again Christians, the decline was similarly steep, from 14 percent in 2001 to 6 percent in 2002. Barna ... also pegs shifting church demographics—younger adults don't share their parents' and grandparents' convictions about tithing.

... many have argued that this relationship between the Levites and the other tribes of Israel prefigures how Christians should provide for their ministers. This view of tithing, known as parallelism, gained prominence in the church around the sixth century.

Many non-Jewish and pre-Christian societies also practiced tithing-like giving. Some ancient sources describe how kings imposed a type of first-fruits tax to maintain holy shrines and support clergy. From Nebuchadnezzar's Babylonia to the temples of Apollo in Delphi and Athena in Athens, pre-Christian centers of worship collected tithes for their gods. Ancient cultures as disparate as the Greeks and Chinese—including the Arabians, Phoenicians, Romans, and Carthaginians—gave in ways mirroring the tithe. Some scholars believe ancient cultures hit on the seemingly arbitrary figure of one-tenth because they often did calculations on their fingers.

The early church's views on tithing foreshadowed many of today's stewardship debates. The Eastern Church began tithing out of obligation because they believed Jesus' conversation with the rich young man demanded sacrificial generosity. Clement of Alexandria and Irenaeus (Church fathers who were mentored directly by the Apostles themselves) pleaded with the church to surpass even the Old Testament tithe since Christ had freed them from the Law.

Later church fathers—John Chrysostom, Cyprian, Origen, and Augustine among them—complained from time to time that their followers lacked Christian charity. Chrysostom even shamed his stingy church for marveling at those who tithed. 

The early church's expectation that every Christian would tithe found formal expression at the Synod of Mâçon in 585, which embedded the practice in canon law. A millennium later, the Council of Trent sharpened this law's teeth: it provided for excommunication if any Catholic declined to contribute his tithe. (And we think we have it bad?!) This, despite the stain in the Church's monetary record that Luther had so recently uncovered in his critique of papal indulgences.

Post-Reformation Europe, however, didn't do much better: in the centuries after Luther, secular governments often acted on behalf of the churches by collecting mandatory tithes. These more closely resembled American property taxes than Jewish monetary offerings.

Without a state-imposed tithe, giving in the United States developed quite differently than in Europe. American church leaders have often emphasized the New Testament's command to give freely and cheerfully, which some leaders have cited to advocate giving less or even more than ten percent. As a result, tithing has been practiced only sporadically in the modern church, though some revival has been seen in recent decades among Baptists and elements of the Wesleyan holiness movement and Pentecostalism." (Bold and parentheses mine).

Read the whole Christian History and Biography article here.