It is often difficult for those of us who are Farmers and Ranchers to see how we can even 'survive' financially from year to year, much less give away the first fruits of our labor as a love offering to God as He told us to do. However; those of us who have done so, have learned that it really is impossible to out give God!
In fact, the only time in Scripture that God tells us to test Him, is in regard to our giving our best back to Him. This is exactly what He did for us when He gave us His only Son to suffer and die in our place, for our sin, so we could inherit eternal life.
In Malachi chapter 3, He says: "Test me in this,and see if I will not throw open the floodgates of Heaven and pour out so much blessing that there will not be room enough to store it." However; God also says that our failure to give Him our best is to "rob" Him!
His promises are not those of a "prosperity Gospel" where we give something to God in exchange for something from Him, as if to purchase His love and our salvation. He wants us to give Him our best that flows from a love relationship with Him and from a heart of gratitude for what He has done for us.