Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
Passover at Sinai. This, as being kept in the first month, was prior in time to the numbering of Num 1:1 ff, and to the other events narrated in this book. It is, however, recorded here as introductory to the ordinance of Num 9:6-14 in this chapter respecting the supplementary Passover; the observance of which was one of the last occurrences during the halt at Sinai.
In some details, the present Passover differed both from that kept at the Exodus itself and from all subsequent Passovers. For example, the direction of Exo 12:22 could not be carried out in the letter while the people were dwelling in tents; and may be regarded as superseded by Lev 17:3-6 (compare Deu 16:5 ff).
In other points, such as how many lambs would be wanted, how the blood of the Paschal victims could be sprinkled upon the altar in the time specified, etc., the administrators of the Law of Moses would here, as elsewhere, have, from the nature of the case, power to order what might be requisite to carry the law into effect.
Certain men - Probably Mishael and Elizaphan, who buried their cousins, Nadab and Abihu, within a week of this Passover Lev 10:4-5.
The later Jews speak of this as the "little Passover." Coming, as it did, a month after the proper Passover, it afforded ample time for a man to purify himself from legal defilement, as also to return from any but a very distant journey. Compare Hezekiah's act Ch2 30:1-3.
According to all the ordinances - i. e. those relating to the Passover lamb, not those concerning the feast, for the Little Passover lasted, according to the Jews, only one day; nor was it held to be needful that at it leaven should be put away out of the houses.
The cloud ... - The phenomenon first appeared at the Exodus itself, Exo 13:21-22. The cloud did not cover the whole structure, but the "tent of the testimony," i. e. the enclosure which contained the "ark of the testimony" Exo 25:16, Exo 25:22, and the holy place. The phenomenon is now again described in connection with the journeyings which are to be narrated in the sequel of the book.
A year - literally, "days," idiomatically a year Lev 25:29, an expression equivalent to "a full period," though not necessarily the period of a year.