Throughout all their journeys, whenever the cloud was taken up from over the tabernacle, the people of Israel would set out.
As when, in the creation, God had finished this earth, which he designed for man's habitation, he made man, and put him in possession of it, so when Moses had finished the tabernacle, which was designed for God's dwelling-place among men, God came and took possession of it.
Commenting on Exodus 40:34-38
when the cloud was taken up from over the tabernacle--In journeying through the sandy, trackless deserts of the East, the use of torches, exhibiting a cloud of smoke by day and of fire by night, has been resorted to from time immemorial. The armies of Darius and Alexander were conducted on their marches in this manner [FABER].
When the cloud was taken up - The subject of these three last verses has been very largely explained in the notes on Exo 13:21, to which, as well as to the general remarks on that chapter, the reader is requested immediately to refer. See Clarke's note on Exo 13:21.