Exodus 12

With the introduction of the passover, Moses instructed -

"...ye shall observe this thing for an ordinance to thee and to thy sons for ever." (Old Testament | Exodus 12:24)

And then Moses explains why -

"...it shall come to pass, when your children shall say unto you, What mean ye by this service?
27 That ye shall say, It is the sacrifice of the LORD's passover, who passed over the houses of the children of Israel in Egypt, when he smote the Egyptians, and delivered our houses. And the people bowed the head and worshipped." (Old Testament | Exodus 12:26 - 27)

Such ordinances were introduced to keep their mind on the mark, the coming of and the atoning sacrifice of Jesus Christ. During His mortal ministry, even during the passover, the Savior introduced a new ordinance of the sacrament of the emblems of His flesh and blood. The ordinance by which our children may ask "What mean ye by this service". It is during this ordinance of our day, where we bow our heads weekly, and remember and worship Him.