The following "sermon" is from a Biblical perspective only (which should cover all Jews - tithing began with Abram back in Genesis! - and Bible-believing Christian denominations including Catholicism, etc). If you do not share the same faith, then do not jump up and yell at me - just take this as an opportunity to learn about something different from you. If you do share the Christian faith, then do not get upset with me because nothing I am about to say is based on anything other than scripture, so if you have a problem with it then you have a problem with God, not with me. Don't shoot the messenger, as the saying goes...

(I can come across sounding a bit harsh at times, I know, but that is not my intent here. I'm merely laying it out on the line in very plain black & white.

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As commanded by God, we tithe 10% of our gross pay every paycheck (Btw, "Tithe" means 10%, it isn't just a word). Beyond that, we contribute a small amount extra to our church building fund to help pay for the new building we recently constructed. Why? Because God said to and because He is faithful in proving - when we tithe, God will provide all of our needs - not all of our wants, but everything we truly need.
And that is where so many people run into problems. I see many of you saying "I wish we could tithe, but we can't afford it..." That's not true. You likely can't afford it only because you are being a poor steward of the money God has given you. There are extreme circumstances, of course, and God would never punish us in those extreme circumstances as long as our hearts are still in the right place, but most people could easily tithe if they wanted to. DW just recently graduated from college and currently still only has a part-time job, and my job pays less than most starting school teachers make in the U.S. these days, even though it is a good job. And yet somehow we are still able to tithe and live comfortably in a modest appartment with modest cars, etc. So many people I see comlaining about money are the same ones who live in large houses in expensive neighborhoods, who drive multiple cars that have payments in the $500-$1000 per month range, who eat out at nice restaurants regularly if not most nights, who spend a lot of money on entertainment and home electronics, etc. The fact that they "can't afford to tithe" has nothing at all to do with how much money they make and everything to do with the fact that their own selfish desires for "stuff" and hedonistic pleasure outweigh their willingness to give anything back to God. "The love of money is the root of all kinds of evil." So most people are so greedy and selfish that they aren't even willing to give back such a small part of what God allows them to have, they get more and more wrapped up in living beyond their means, and in general nothing good ever comes out of it. I can say this because it is only reasonable to assume that if you "can't afford to tithe" that you likewise can't afford to donate to charities or help those in need. So what good is your wealth doing anyone beside yourself? Is that not the definition of selfishness?
The only way anyone will ever "afford" to tithe is to make it a priority. You can afford to pay for your house and your car and your electric bill. Why? You make them priorities. It is the same with tithing. I know automatically that our tithe is X amount of dollars each paycheck, and that amount is accounted for immediately. You cannot be a faithful tither by spending all of your money on other things and hoping you have enough left over in the end. Let's face it - we all would just spend the entire amount and have nothing left! No, you take it out up front and adjust your living accordingly. Maybe you eat at home more often, go to movies less often, trade in your BMW for a Toyota, stop lusting after that 3,000 sq. ft mansion in the ritzy neighborhood when you know full well that you don't truly need to live in that location in order to survive or be happy. We don't drive fancy cars or live in a fancy new house or a nice neighborhoo, we don't have cable or a big screen HDTV, but we are happy and don't NEED those things to stay happy. It is amazing how little you miss that 10% when you know where it is going automatically and up front and completely ignore it as part of your income.
Someone earlier said that to tithe would cost them around $600 a month and they can't afford it. Let's use that example. (Sorry if it sounds like I am picking on a specific person - I'm not... it's just an example for illustration purposes.) If $600 = 10% of someones gross pay, then they are making around $72,000 a year. Cry me a river! That would triple our current annual income! If we can afford to tithe on 1/3 of a $72,000 salary, then honestly there is likely no excuse for a $72,000/yr salary person to not be able to afford it. The only excuse is that people spend all of their money on other things that mean more to them, and if they then claim to be devoted to God they are lying because their actions very much outweigh their words and their words are empty and meaningless. If you are truly devoted to God then your life and your actions will show it, and that includes making decisions about your priorities such as tithing. We must first abandon our love of money and come to see it for what it truly is - a tool for commerce, not the be all and end all of our existence. A good financial planner will tell you that if you are going to save for retirement then you must save up front before you pay your bills or else you will spend everything and have nothing left to save. It is the same with tithing. If you are going to store up treasures on Earth, at least store up treasures in Heaven where moth and rust will not destroy!
I also beleive that tithing goes beyond simple money. If God has given us a special talent we should likewise give back in portion from that talent. My DW and I both play instruments so we play in our church orchestra. My MIL is the pianist. My family sing in the choir. Some people teach sunday school classes or lead prayer groups. If you have a talent that can be used by God in the church, then offer it up the same way you would money as a tithe.
If any of the above offends a fellow Christian because you think it is stepping on your toes and makes you feel bad, then tough - sometimes we are supposed to have our toes stepped upon and to feel bad in order to bring to light to our hearts those areas where our lives are falling short of the full purpose of the glory of God that He has prescribed for us to reach. If anything I have written is false, prove it with scripture, don't just attack because you don't "like" it. Not liking something does not change its veracity. I don't like having to drive the speed limit, but that doesn't change the law so I do it anyway. We can dislike many truths, but they will still be truths.
It is written in Malachi 3:10, "Bring the whole tithe into the storehouse, that there may be food in my house. Test me in this," says the Lord Almighty, "and see if I will not throw open the floodgates of heaven and pour out so much blessing that you will not have room enough for it." To God, "blessing" does not necessarily equal more money, though many of us would like to think so! Blessings come in many forms. So don't tithe because you think God will make you rich (or richer) because that would be false and would stem from greed, not from a love for God and a desire to do His will and follow His commandments. Tithe out of joy

for giving something back as an offering in recognition of all of God's blessings!