Three times a year all your men must appear before the LORD your God at the place he will choose: at the Feast of Unleavened Bread, the Feast of Weeks and the Feast of Tabernacles. No man should appear before the LORD empty-handed: Each of you must bring a gift in proportion to the way the LORD your God has blessed you. Deuteronomy 16:16-17
“Each man was to bring a gift because the keynote of each of the festivals was the joyful expression of thanks for God’s rich spiritual and material blessings experienced in the past and the present. The gifts to the LORD were to be proportionate to the people’s blessings.”
Jack S. Deere on Deuteronomy 16:16-17 in The Bible Knowledge Commentary.