Exodus 40:2

On the first day of the first month. — The Israelites had quitted Egypt on the fourteenth day of the first month, Abib (Exodus 12:6). They had reached the wilderness of Sinai in the course of the third month, Sivan, and encamped in front of Sinai shortly after (Exodus 19:1). The two long absences of Moses in the Mount had occupied nearly three months, and were separated by an interval probably of several days. It must have been the sixth or seventh month before the work was commenced, and very late in the year — the eleventh or twelfth month — before it was accomplished. Hence, the new year was now approaching, and, as it was approaching, its first day was naturally chosen as most fit for the inauguration of the new structure.

The tabernacle of the tent of the congregation. — Rather, the tabernacle, the tent of meeting. The words mishhan and ‘ohel are in apposition, not in regimen. (So also in Exodus 40:6.)