It goes back to the law of Moses, and even further past that to Abraham. (Gen. 14:20 (18–20); Mal. 3:10 (8–10), Nehemiah 10:37) We believe tithing is an eternal principle as well.
The concept is simple. God has given us everything. All he asks is a tenth of our increase in return. In ancient times, this tenth was usually given in the form of livestock. The Levites, who did not have a land of inheritance of their own, would sacrifice part of this offering in a symbolic manner that was to prepare the minds of the Israelites to prepare for Christ, and then the rest was used to feed the Levite families. None of the sacrifice was wasted and it was treated as a sacred offering.
Today, we usually use money because that is now how we calculate increase and Christ fulfilled the law of Moses, ending sacrifice by the shedding of animal blood. Now, instead we are asked to give our hearts to him. Tithing is a way that we do that.
Tithing is treated in a very sacred manner by our church. We do not have a paid clergy. Thus, tithing doesn't go to line anyone's pocket. The committee who decides how to use the funds are very aware of the widow's mite (meaning that some people have hardly nothing and still do their best to pay tithing). They carefully and prayerfully consider where the funds from tithing should be used and how best they will build of the Kingdom of God. This money is God's money and should be used as such. Thus, often the funds go to help build churches and temples in places where the people wouldn't be able to afford to build one otherwise. Some of the funds go to help latter-day-saint youth with their schooling.
The heads of our church do not get rich on our tithing. In fact, they never see a penny of it.
If you want more information on where our tithes go, here is a link.
However, it is not really a sacrifice for the saints. The Lord never requires anything of his people without giving them great blessings in return. As is promised in Malachi 3:10-12:
There are some pretty awesome blessings there, and I can promise that the Lord never lies. If He says He will do something, it is going to happen.10 Bring ye all the tithes into the storehouse, that there may be meat in mine house, and prove me now herewith, saith the Lord of hosts, if I will not open you the windows of heaven, and pour you out a blessing, that there shall not be room enough to receive it.11 And I will rebuke the devourer for your sakes, and he shall not destroy the fruits of your ground; neither shall your vine cast her fruit before the time in the field, saith the Lord of hosts.
I have experienced the blessings of tithing on numerous occasions. When Grig and I were married, we decided we didn't want to wait to have children. We felt very strongly that we weren't supposed to wait. So, we weren't very surprised when a short time later we found out we were pregnant. We were both working part-time jobs and going to school full-time, but we felt as though everything was going to be okay. (Not just okay, we were super thrilled!)
We both paid our tithing each week and tried our best to keep the rest of the commandments. We carefully saved our money and did our best to be frugal with the rest of it.
When I gave birth to Kevin, it was a very difficult birth, and I ended up having to have a c-section. For those of you who don't know, c-sections are quite expensive. However, somehow in the next two months, we paid off all of our hospital bills. We did have insurance, but it only covered part of the cost. I still don't know where the rest of the money came from, but I do know to give credit to my Father in Heaven and I know it was a direct blessing from paying our tithing. When we follow his commandments, He blesses us. Sometimes we don't recognize the blessings, but they are still there.
Tithing may seem difficult to pay, but it really isn't. Everything we have is from the Lord anyway, so why would it be a sacrifice to give it back to him? Especially when he returns it ten-fold?
I know tithing is a principle of the Lord and that He is mindful of our sacrifices. I have felt the hand of the Lord in my life as I have lived this commandment. It has brought great blessings to our family. We are grateful for the law of tithing.