Genesis 4:3-5 New International Version (NIV)
3 In the course of time Cain brought some of the fruits of the soil as an offering to the Lord. 4 And Abel also brought an offering—fat portions from some of the firstborn of his flock. The Lord looked with favor on Abel and his offering, 5 but on Cain and his offering he did not look with favor. So Cain was very angry, and his face was downcast.
The Bible does not say why God did not accept Cain’s gift. It could have been that Cain’s attitude was not proper, or it could have been that the gift itself that was given by Cain was not up to the standard that is needed to be a proper gift. In Proverbs 21:27 it says, “The sacrifice of an evil person is detestable, especially when it is offered with wrong motives.” God looks at our motives and the quality of what is offered to him. It is important to remember that when you give to God and others, you need to have a joyful heart. Do not worry about how much you are giving up when you give to God. Remember, all things are God’s in the first place. Be joyful when you give God your best in time, tithe, money, possessions, and talents.