Cormack, the giving is twofold. Firstly it is a physical action that prioritises God, and reduces the hold money has over your life. You're giving it away. In giving it away it doesn't own you.
Jesus said you cannot worship God and money, so it's an important thing to do.
Secondly, (and more contentiously) there is the school of thought that suggests God is more able to bestow physical blessings on one who is physically blessing others.
It is said "you reap what you sow". If you are giving friendship, love and encouragement to others, the odds are you will recieve in kind.
The argument is that God is less likely to bless someone with finances that holds onto money very tightly, because it's a dead end. Wheras if you are giving it, there is a flow.
The last point centres around "prosperity doctrine", one which is not universally accepted in the Christian church.
However, the point remains that giving changes YOU. Giving to God is a benefit of itself regardless what happens to it after that point.
The second benefit of giving is that it enables pastors, social worskers and others employed by the church, to devote their time studying the bible, assisting people in need, counselling, preaching, writing and everything else.
Most church employees receive a set wage. A percentage of what is receved by a church, nowhere near the total amount. As such, do we disdain a man for spending some of that wage on a gift of love for his wife? If the church has agreed on an amount they want to bless their pastor with each week, is it not his discretion what he does with that money? If he buys his wife something, it's at the expense of something for himself.
I've been employed by various churches to record albums for them in the past. The music glorifies God, the church grows, they use the recordings to bless people in their church. I don't charge anywhere near what I should for a job like that, precisely because the money comes from peoples tithes and offerings.
However, the time I spend on a record is at the expense of time spent making money to pay for my rent. So it's understandable if I spend any money given to me on paying my rent is it not?
If I forgo certain things to give something to a woman I love, how is that wrong? Is not she receiving a blessing from a blessing I received because of a blessing I gave to God and the church?