The answer to this question is entasis.
Entasis is a design principle in architecture where in a convex curve was applied to a surface which also serves a strength to the construction and it also gives an optical illusion to it. Egyptian pyramids use this design principle.
The writer of the Book of Deuteronomy set the story into the framework of three sermons by Moses to the Israelites as they stand on the plains of Moab poised to cross the Jordan River and enter the Promised Land.
