Exodus 13:18

ויסב means HE LED THE PEOPLE ABOUT from the direct route to a circuitous route. ים סוף is the same as לים סוף TO THE RED SEA. The word סוף has the meaning of a marshy tract in which reeds grow; examples are: (Exodus 2:3) “She placed him in the reeds (בסוף)”; (Isaiah 19:6) “The flags and the reeds (וסוף) shall wither”. וחמשים — The word חמשים means provided with weapons (Mekhilta). — [Because He led them by a circuitous route through the wilderness He brought it about that they went up from Egypt well-provided; for had He led them circuitously by the route of an inhabited district they would not have provided for themselves every thing that they needed, but only a part, like a person who is travelling from place to place and intends to purchase there whatever he will require. But if he were setting out for the wilderness he must provide all that he will require. — This verse (statement in the verse) is written only with the view of making the ear understand (preparing you for a later statement) viz., that you should not wonder with regard to the war with Amalek and the war with Sihon and Og and Midian where they obtained weapons, since they smote them with the sword]. In a similar sense it says, (Joshua 1:14) “and ye shall pass over armed (חמשים)”. Onkelos, too, translated it by מזרזין which signifies “armed” in Aramaic, just as he translates the word וירק in (Genesis 14:14) וירק את חניכיו which means, “And he armed his trained servants” by וזריז. Another explanation of חמשים is: only one out of five (חמשה) went forth from Egypt, and four parts of the people died during the three days of darkness because they were unworthy of being delivered (Mekhilta; cf. Rashi on 10:22).

וַיַּסֵּ֨ב אֱלֹהִ֧ים ׀ אֶת־הָעָ֛ם דֶּ֥רֶךְ הַמִּדְבָּ֖ר יַם־ס֑וּף וַחֲמֻשִׁ֛ים עָל֥וּ בְנֵי־יִשְׂרָאֵ֖ל מֵאֶ֥רֶץ מִצְרָֽיִם׃

but God led the people about, through the way of the wilderness of the Sea of Suf: and the children of Yisra᾽el went up armed out of the land of Miżrayim.