If I owned a store and advertised 10% off all merchandise, how would most people take it? You and I both know it would be considered it a joke. I would have wasted my advertising dollar.
Yet when you ask people to give up 10% for the Lord in whom they profess to believe, they squeal like Justin Bieber. (I'm not letting my atheist and agnostic friends off the hook either. How many of you consider 10 percent more than enough when it comes to tipping a waiter or waitress?)
There are times when I'm dickering with someone over the price of a guitar and I feel like saying, "How 'bout if I just sell it to you at 10 percent over cost? I don't need a stupid commission. I know you don't need money, and neither do I. Better yet, how 'bout if I just give it to you? Your happiness is important to me."
God's grace, of course, is free. Unfortunately, it's a lot more abstract than a wide-screen TV.
Full disclosure: Like most people, I have thus far lacked the nerve to tithe. My church is not a place where you hear the word "should" all the time.