Proverbs 11:24-25 (NIV)
24 One person gives freely, yet gains even more; another withholds unduly, but comes to poverty.
25 A generous person will prosper; whoever refreshes others will be refreshed.

“Divine wisdom has appointed, in the plan of salvation, the law of action and reaction, making the work of beneficence, in all its branches, twice blessed. He who gives to the needy blesses others, and is blessed himself in a still greater degree.
 

The Glory of the Gospel

That man might not lose the blessed results of benevolence, our Redeemer formed the plan of enlisting him as His coworker. God could have reached His object in saving sinners without the aid of man; but He knew that man could not be happy without acting a part in the great work. By a chain of circumstances which would call forth his charities, He bestows upon man the best means of cultivating benevolence, and keeps him habitually giving to help the poor and to advance His cause. By its necessities a ruined world is drawing forth from us talents of means and of influence, to present to men and women the truth, of which they are in perishing need. And as we heed these calls, by labor and by acts of benevolence, we are assimilated to the image of Him who for our sakes became poor. In bestowing, we bless others, and thus accumulate true riches.

It is the glory of the gospel that it is founded upon the principle of restoring in the fallen race the divine image by a constant manifestation of benevolence. This work began in the heavenly courts. There God gave to human beings an unmistakable evidence of the love with which He regarded them. He “so loved the world, that He gave His only-begotten Son, that whosoever believeth in Him should not perish, but have everlasting life.” John 3:16. The gift of Christ reveals the Father’s heart. It testifies that, having undertaken our redemption, He will spare nothing, however dear, which is necessary to the completion of His work.” CS p. 14

That’s why we give!