Verses 17-19:
The shortest, most logical route from Egypt to Palestine lay along the Mediterranean sea-coast. One traveling from Tanis to Palestine would travel almost due east to Pelusium, then to Rhinocolura, and along the coast to Gaza, Ashkelon, and Ashdod. The marsh region between Tanis and Pelusium was, during the 18th and 19th Dynasties, surmounted with an embankment causeway connecting the two cities.
God chose not to lead Israel by the shortest, most common route. He led them by a circular route, south from Tanis then east, through the Sinai Peninsula. The purpose: Israel was newly-freed people, ill-equipped for the fighting they would encounter. They had no codified system of law by which they were regulated. They must learn the necessary military skills, become hardened by the travels and trials encountered in the Sinai; and most important, they must have a law to regulate their government and society. All they experienced in the Sinai would be useful in their preparation to possess the Land. And this could only be gained by the time spent in the desert.
This illustrates God’s leadership today. He may not always lead in the way that seems logical to men, see Isa 55:8, 9. But He always leads in the way that is best for His obedient child.
"Harnessed" chamusim, the only occurrence of this Hebrew word in the Old Testament. It means "girded," or "armored." A military term, it suggests that Israel’s march was in military order. The term is related to khamesh, "five," which suggests that in the initial march, the people were divided into five groups
Moses fulfilled the last request which Joseph made years earlier, cf. Ge 50:25, 26. The coffin carrying Joseph’s remains accompanied Israel on their journey from Egypt to the Land of Promise.