For all they did cast in of their abundance; but she of her want did cast in all that she had, even all her living. Mark 12:44.
Some people consider tithing an Old Testament teaching. They think that when Jesus told the Pharisees that they tithed mint, and small things like that, and neglected the bigger things, He was downgrading the idea of tithing. But Jesus made it clear that while we ought to do the one thing, we should not leave the other undone either.
One day a widow woman came to the Temple and put into the offering container only two mites. From that experience Jesus drew some important lessons concerning giving. One of them was this--that heaven places value upon the gift in an entirely different way than we do. Jesus said that this woman put in more than all the rest. How can that be? Because God measures our giving not by how much we give, but rather by how much we have left after we have given. So if someone puts in $10,000, and has $10,000 left, he has given far less than one who put in 2 cents and has nothing left.
Of course, it is possible to give all the cash you have and still own a house in the city and a house in the country, and a boat in the harbor, and three new cars! Our possessions are to be considered also when we figure out how much we have left. 1 Corinthians 4:7 says, "What hast thou that thou didst not receive? now if thou didst receive it, why dost thou glory, as if thou hadst not received it?" Whatever our wealth, be it money or possessions, it is God that gave the power to get it (Deut. 8:18), and thus He has a claim upon all that we have been given.
The first portion of our money that is the Lord's in a special sense is the tithe. But we have not finished when we have returned our tithes to the Lord. He has invited us to bring our freewill offerings as well. Malachi 3:8 says that God has been robbed in tithes and offerings. And even beyond that, God has a claim on all that we possess. "Some think that only a portion of their means is the Lord's. When they have set apart a portion for religious and charitable purposes, they regard the remainder as their own, to be used as they see fit. But in this they mistake. All we possess is the Lord's, and we are accountable to Him for the use we make of it."--Christ's Object Lessons, p. 351.