Exodus 12:1

The Lord spake. Regulations pertaining to the first of the so-called Mosaic institutions are recorded in this chapter. It should be noticed that neither Moses nor Aaron introduced legislation of his own, either here or later. The whole religious and civil system announced to Israel by Moses before the Exodus, and after, was revealed to him. He was not the originator of the laws in the Pentateuch that bear his name, but merely the appointed instalment through which God’s will was made known to His people.

In the land of Egypt. Since the greater part of the Mosaic legislation was given at Mt. Sinai, Moses emphasizes that this ordinance, the Passover, was instituted prior to the Exodus.