what are the reasons for christian giving?

First and foremost, it is God who gave His best to us – His Son Jesus Christ.

Now, we have the privilege and the honor of giving back to Him as an act of trust and faith – not because He needs it.

Matthew 6:3-4 When you give to the poor, do not let your left hand know what your right hand is doing, so that your giving will be in secret; and your Father who sees what is done in secret will reward you.

1 Corinthians 16:1-2 Now concerning the collection for the saints, as I directed the churches of Galatia, so do you also. On the first day of every week each one of you is to put aside and save, as he may prosper, so that no collections be made when I come.

2 Corinthians 9:7 Each one must do just as he has purposed in his heart, not grudgingly or under compulsion, for God loves a cheerful giver.

Some Biblical principles to follow:
God expects His people to give (Matt 6:2); for His glory and for the good of His people (Matt 6:1); as an act of worship (1 Cor 16:2); driven by the gospel (2 Cor 8:9, 12) to give as much as we can (2 Cor 9:6); willingly, freely, and cheerfully (2 Cor 9:7).