Commentary for Numbers 1:1

וידבר… במדבר סיני … באחד לחדש וגו׳ AND [THE LORD] SPOKE [UNTO MOSES] IN THE DESERT OF SINAI … ON THE FIRST DAY OF THE [SECOND] MONTH … [TAKE YE THE SUM OF ALL THE CONGREGATION] etc. — Because they were dear to him, He counts them every now and then: when they went forth from Egypt He counted them (Exodus 12:37), when many of them fell in consequence of their having worshipped the golden calf He counted them to ascertain the number of those left (cf. Rashi Exodus 30:16); when he was about to make His Shechinah dwell amongst them (i. e. when He commanded them to make a Tabernacle), He again took their census; for on the first day of Nisan the Tabernacle was erected (Exodus 40:2) and shortly afterwards, on the first day of Iyar, He counted them.

AND THE ETERNAL SPOKE UNTO MOSES IN THE WILDERNESS OF SINAI, IN THE TENT OF MEETING. Because He had interrupted with the commandments about the Sabbatical year and the Jubilee, of which He said that they were spoken in Mount Sinai¹²Leviticus 25:1. [in contrast to all the other commandments in the Book of Leviticus, which, as mentioned at the beginning of that book, G-d told Moses from the Tent of Meeting], He stated here again that this communication was given from the Tent of Meeting, as were all the communications which He had mentioned since the beginning of the Book of Leviticus. And all of them from now onwards [were said to Moses] from the Tent of Meeting, for since the time that the Tabernacle was set up and G-d called him [Moses] from the Tent of Meeting,¹³Ibid., 1:1. He only communicated with him from there.
Scripture mentions here in the wilderness of Sinai in order to tell us that they did not travel away from there until they were counted [the first time, as described here], for the second census¹⁴Further, 26:1-51. was taken in the plains of Moab,¹⁵Ibid., Verse 3. but the [actual] communication was in the Tent of Meeting.

"In the Sinai Desert..." Our Rabbis expounded precious understandings through this text in Bamidbar Rabbah 1. It is only left to ask why HaShem did not use consistent measures in this verse. When it describes where they were, the general location (the Sinai Desert) is mentioned first and only afterwards does it specific 'in the Tent of Meeting;' but when it mentions the time the specific is mentioned first, 'on the first day of the second month,' and afterwards the general - 'in the second year.'
It appears, actually, that in a very intelligent fashion the verse did use consistent measures. This can be understood in the same way they explain "...see there is a place near Me..." (Shemot 33:21) in Bereshit Rabbah 68, saying 'that the place of the Holy One is secondary to Him.' From this perspective, every place is secondary in relation to the place where Gd encamps. Therefore, in our verse, the Tent of Meeting is actually the encompassing measure and the desert is secondary to it. In order that we read the verse from this perspective, the second half was joined to it 'on the first of the month...in the second year.' The phrase 'Tent of Meeting' is actually the encompassing measure, and therefore was placed second just as the words 'second year' were placed afterthe phrase 'on the first day of the month.' You can know how immeasurably awesome is the place where the Lord is from the fact that six hundred thousand men of Israel stood in the two cubits between the poles of the ark (Bereshit Rabbah 5). Though it appears little to the eye, it is great from the perspective of the One who dwells there, Blessed be He.