ויעשו בני ישראל, seeing that the festival of Passover in Egypt had been observed only for a single day, precluding the Israelites from offering all the other sacrifices scheduled for that festival, now that the Tabernacle had become functional the Torah had to instruct that this year the Passover was to be observed in accordance with the legislation recorded in both Leviticus and Deuteronomy where the Torah speaks of the Passover sacrifices which have to be brought when the Passover is observed in future generations.