John Calvin Commentary Exodus 40:17

"And it came to pass in the first month in the second year, on the first day of the month, that the tabernacle was reared up." — Exodus 40:17 (ASV)

And it came to pass in the first month. In all the arrangements that are described here, it must be especially noted that Moses obeyed God in such a way that he did not vary in the smallest detail from the pattern prescribed for him.

Therefore, he so frequently emphasizes the fact that he did as God had commanded him. This was not without reason, for people are more prone to nothing than to mix their own inventions with God’s commands, as if they were wiser than He is. Then, so that the people might know that there was nothing of human invention in all the ceremonial service, Moses so carefully insists on this point and so often testifies to his obedience.

But if so great a prophet dared to attempt nothing of his own in such minor matters, how great is the audacity and arrogance of those who arbitrarily invent innumerable fabrications by which God is to be worshipped! Let us, however, learn from this passage to embrace with reverence whatever has come from God, while we reject whatever people advance of their own.