Giving is a Matter of the Heart
The main principle behind tithing and giving is the fact that what we do with our money shows where our heart is. Matthew 6:21 says "For where your treasure is, there your heart will be also." When we are able to give 10% or more of our income instead of keeping that money for ourselves, it shows that our heart isn't tied to our money and that we love God more than our money. This is a blessing to our lives and something that will help better our lives, as well as help the lives of others.
Why We Give
"In every way I’ve shown you that by laboring like this, it is necessary to help the weak and to keep in mind the words of the Lord Jesus, for He said, ‘It is more blessed to give than to receive.’ ” Acts 20:35
Genuine love for God and growth in the Christian life will result in a mature, giving heart. Indeed, a heart dedicated to Christ cannot help but be generous toward God and his people, often (if not usually) leading us to voluntarily give far more than what was required under the Old Testament tithing regulations.