Why do Mormons give 10% of their income to the church?

So, Members of The Church of Jesus Christ of Latter-day Saints live a commandment called "The Law of Tithing"  In 1838 Joseph Smith received revelation from God that God's people should live this commandment. (Doctrine and Covenants 119)

In this commandment God has asked us to give "One tenth of all their interest annually" this basically means to give 10% of your income to God.  People have asked me on a few occasions "Why does God need your money?" The truth is, He does not need anything from us, as everything belongs to Him anyway. It is less of God needing money, but more of God seeing if our hearts are putting Him above the things of the world.

This is not a new commandment, For example, in Genesis 28:20-22 Jacob makes a vow to God to pay one tenth of all he has to God.   Jacob saw that the things that God had given him were a gift from God and so he made this vow to God.

Malachi 3:8-12 Teaches us that by keeping this commandment God will "Open the windows of heaven, and our you out a blessing, that there shall be not room enough to receive it" And this is true, As with all of Gods commandments God has promised us blessings for keeping them, we just need to exercise faith in Him in order to receive those blessings. The best way to find out that this is true is to do as God says and "Prove me now herewith" and just try it out.

So what does the church do with this money? The money is gathered together, and is used as the Lord directs by the decision of the leaders of the church (Doctrine and Covenants 120) It is spent on, Building Temples, meeting houses (Chapels), Funding the missionary programme (This does not include expenses  of the individual  missionaries) Preparing materials used in classes IE Books and Hymn Books, Temple and family history work,  and education.

The leaders of the church support themselves from their jobs, and so it does not go to pay people as local ministers. So, the tithing does not go to support local ministers, but to support the organisation of the church as a whole and to support the needs of people who struggle with their lives.

The tithing is paid at the discretion of the individual, You simply put your donation in an envelope and give the envelope to the bishop, There is no tray, nobody will ask you if you have paid tithing, it is simply between you and God. Once a year the bishop will meet with the member of the church to give them a slip of paper with all of the contributions they have made during that year. You are asked if you are a full tithe payer, you can answer yes or no, Nothing more will be asked about it.

People who are not members of the church are not asked to give any donations at all. But if they choose they may donate to specific things like the humanitarian aid programme and other services the church provides.