highway - such a causeway (raised way, from a Hebrew root, “to cast up”) as was used for the march of armies; valleys being filled up, hills and other obstructions removed (Isa 62:10; compare Isa 40:3, Isa 40:4).
way of holiness - Hebraism for “the holy way.” Horsley translates, “the way of the Holy One;” but the words that follow, and Isa 35:10, show it is the way leading the redeemed back to Jerusalem, both the literal and the heavenly (Isa 52:1; Joe 3:17; Rev 21:27); still Christ at His coming again shall be the Leader on the way, for which reason it is called, “The way of the Lord” (Isa 40:3; Mal 3:1).
it shall be for those: the wayfaring men - rather, “He (the Holy One) shall be with them, walking in the way” [Horsley].
though fools - rather, “And (even) fools,” that is, the simple shall not go astray, namely, because “He shall be with them” (Mat 11:25; 1Co 1:26-28).