Who are the blind that He will lead?
Rashi: They are Yisrael, who were blind until now and did not look at Me.
Radak: Yisrael in Galus.
On which path will he lead them?
Rashi: On the good path, which they did not know to go on it.
Radak: I will lead them on a path that they did not know - I will lead them to their land via the Midbar of the nations.
Malbim: He will remove the mountains that block the straight path. This is like "Kol Ge Yinasei" (40:4).
Why does it say "l'Or"?
Radak: One who walks in darkness, or on a crooked path, he stumbles. One who walks on a path that he did not know, it is as if he walks in darkness, or on a crooked path. Yisrael will go like one who goes in light, and on a straight path.
Malbim: A blind person can go on a path by himself if he is used to it. I will lead them on new roads and minor paths that they did not know, and help them to go by themselves. Three things can block a person from finding the right path. (a) He is blind - therefore it says "I will lead the blind." (b) Darkness - "I will make the darkness light in front of them." (c) If the path his crooked - "I will make the crooked straight."
Did Hashem already do so?
Rashi: He will do so. Nevu'ah often discusses the future as if it already happened.
Malbim: This refers to "was I silent from of old, that I will be silent also now?" (14) No - just like I always did, so I will do now!
