Charles Ellicott Commentary Numbers 28:16-17

"And in the first month, on the fourteenth day of the month, is Jehovah`s passover. And on the fifteenth day of this month shall be a feast: seven days shall unleavened bread be eaten." — Numbers 28:16-17 (ASV)

And in the fourteenth day of the first month ... — The observance of the Passover had been suspended for thirty-eight years. The law is now proclaimed anew. The observance of the first and seventh days of the feast is commanded in Exodus 12:16 and Leviticus 23:7-8; and in Leviticus 23:7-8, it is also commanded that an offering made by fire should be offered for seven days. The nature of that offering is stated in the 19th verse of this chapter, and the fact that these details are not found in Leviticus 23 may be cited as proof of the prospective character of much of the Levitical legislation.