Adam Clarke on Exodus 40:2

The first day of the first month - It Is generally supposed that the Israelites began the work of the tabernacle about the sixth month after they had left Egypt; and as the work was finished about the end of the first year of their exodus, (for it was set up the first day of the second year), that therefore they had spent about six months in making it: so that the tabernacle was erected one year all but fifteen days after they had left Egypt. Such a building, with such a profusion of curious and costly workmanship, was never got up in so short a time. But it was the work of the Lord, and the people did service as unto the Lord; for the people had a mind to work.