When we give God back the tithe that is His to begin with, He blesses us abundantly spiritually and physically. Notice that God says He commands tithes so "that there may be food in My house" (Malachi 3:10). Tithes are primarily used to feed His people spiritually! If we support the work God is doing through His faithful ministers, He promises to bless us far above anything we could imagine (Ephesians 3:20-21)!
By paying to God what we owe Him (that is, His tithes), He rewards us with blessings. Christians often find their third tithe years to be abundant with all types of blessings and invaluable lessons learned. These are not always material blessings, however. Storing up spiritual treasures in heaven is far more important than physical prosperity. God does not promise to make us wealthy but that our relationship with Him will prosper. Such eternal blessings are far greater than any temporary physical blessings we could receive.