It is a night of solemn observance to the LORD for bringing them out of the land of Egypt. This is that night of the LORD, a solemn observance for all the children of Israel throughout their generations.
Exodus 12:42
Surrounding context
12:41 And it came to pass at the end of the four hundred and thirty years--on that very same day--it came to pass that all the armies of the LORD went out from the land of Egypt.
12:42 It is a night of solemn observance to the LORD for bringing them out of the land of Egypt. This is that night of the LORD, a solemn observance for all the children of Israel throughout their generations.
12:43 And the LORD said to Moses and Aaron, "This is the ordinance of the Passover: No foreigner shall eat it.