We should give from our “first fruits”, and not merely from the amount that is “left over” after we spend our money on other things. When we give to God first, it sets the proper priority for our saving and spending.


Honor the Lord with your wealth, with the firstfruits of all your crops.  
Proverbs 3:9

Bring the best of the firstfruits of your soil to the house of the Lord your God.  Exodus 23:19

So do not worry, saying, “What shall we eat?” or “What shall we drink?” or “What shall we wear?” For the pagans run after all these things, and your heavenly Father knows that you need them. But seek first his kingdom and his righteousness, and all these things will be given to you as well.  Matthew 6:31-33 

We should give in proportion to our earnings. 

Each of you must bring a gift in proportion to the way the Lord your God has blessed you.  Exodus 16:17 

But since you excel in everything—in faith, in speech, in knowledge, in complete earnestness and in the love we have kindled in you —see that you also excel in this grace of giving. . . . Now finish the work, so that your eager willingness to do it may be matched by your completion of it, according to your means. For if the willingness is there, the gift is acceptable according to what one has, not according to what one does not have.  2 Corinthians 8:7, 11-12