Why does it say "Maslul" and "Derech"?
Malbim: Derech is a public path. By it will be a Maslul paved also for individuals who go on the side of the road.
For whom is the Derech?
Rashi: It is for passersby.
Malbim: Refer to 35:8:1:1.
What is the Chidush that there will be a path there?
Radak: There was never a path there in the Midbar. Now, there will be a path.
Radak citing a Midrash: Now, there is no path in the Midbar. It is all sand, and a caravan goes at night only via light of the constellations. Then there will be a path. Maslul is like Mesilah.
Why will it be called "Derech ha'Kodesh"?
Radak: The Am Kadosh will go on it.
What is the meaning of "Lo Ya'avrenu Tamei"?
Radak: No Rasha will go on it.
Malbim: This is to distinguish from Yishmaelim, who have a road in the Midbar to their Navi, which they call Derech ha'Kodesh. Those who go on this path will guard from all Tum'ah.
Why does it say "v'Hu Lamo"?
Rashi: It is the path for the blind, deaf, lame and mute mentioned above.
Radak: It is only for Yisrael.
What do we learn from "Holech Derech ve'Evilim Lo Yis'u"?
Rashi: Even fools will not stray from the path, for I will straighten it in front of them.
Radak: Both one who normally goes on paths, and Evilim, they will not err on that path; they will go straight to Yerushalayim. Evilim are fools regarding paths that they are not used to.
Malbim: Until now, one who went in the Midbar needed (a) to go in caravans of many people, and (b) to take with them a guide to show the way. However, then, even one who goes on a Derech alone, and even Evilim who do not know the way, will not stray, for the path will be straight.