'Ceremony' in the Bible

When you enter the land that the Lord will give to you, just as he said, you must observe this ceremony.

When your children ask you, 'What does this ceremony mean to you?' --

When the Lord brings you to the land of the Canaanites, Hittites, Amorites, Hivites, and Jebusites, which he swore to your fathers to give you, a land flowing with milk and honey, then you will keep this ceremony in this month.