Why does it say that your ears will hear?
Rashi: This is unlike you do now, that you despise his word, and say "Lo Sechezu Lanu Nechochos" (10). Rather, your ears will lean even in back of you to hear a word from Me.
Radak: Even if the teacher will call to you from in back of you, and tell you 'this is the path; go on it', your ears will hear and heed, and all the more so if he commands you face to face. This is Chizkiyah's generation, who wanted to guard Torah and Mitzvos.
Malbim: The verse depicts that the guide, i.e. the Navi, goes in front of them to lead them in Hashem's way. The nation goes in back of him and looks at his path. If sometimes also the guide errs to the right or left from the straight path, your ears will hear a word from in back of you to correct you. Hashem will supervise lest you err due to the Navi's error. He Himself will arouse you about the straight path 1 !
Why would Hashem not arouse the Navi, who is at the proper level to receive Hashem's word? (PF)
What is the significance of right and left?
Rashi: You lean your ears to hear - perhaps a Navi will come and teach you a way to go between right and left.
Radak: When you want to turn right or left, do not do so. Rather, the path is straight in front of you - go on it, and do not veer right or left from Mitzvos of the Torah. It is as if it is written Teiminu with a Yud; the Aleph is in place of a Yud.
Malbim: Refer to 30:21:1:3.
