Shall hear — Thou shalt hear the voice of God's word and spirit. Behind thee — A metaphor borrowed from shepherds, who use to follow their sheep, and recall them when they go out of the way.
Related Commentaries of Isaiah 30:21
Isaiah 30:21
21 And thine ears shall hear a word behind thee, saying, This is the way, walk ye in it, when ye turn to the right hand, and when ye turn to the left.