The Catechism in Questions & Answers

713. What is the significance of Thanksgiving Day?

Thanksgiving Day is the celebration when we give thanks to God as the Creator.
On one Sunday of the year—Thanksgiving Sunday—a divine service is held which focuses on expressing gratitude to God for all the good gifts He grants to us human beings.
Out of thankfulness to Him, believers bring a special offering to Him: “Whoever offers praise glorifies Me; and to him who orders his conduct aright, I will show the salvation of God” (Psalm 50: 23).