John Gill's Exposition of the Whole Bible
Isaiah 30:21
And thine ears shall hear a word behind thee,.... Which may be said in reference to the backsliding and declining state of the people, Isaiah 30:11 and is thought by some to be an allusion to schoolmasters, who stand behind their scholars, or at their backs, to guide, teach, and instruct them; and by others to shepherds following their flocks, who, when they observe any of the sheep going out of the way, call them back; or to travellers, who, coming to a place where are several ways, and being at a loss which way to take, and inclining to turn to the right or left, are called to by persons behind them, and directed in the right way. This "voice behind" is by the Jews e interpreted of Bath Kol; and by others of the voice of conscience; but it rather intends the Spirit of God, and his grace; though it seems best to understand it of the Scriptures of truth, the word of God, the only rule of faith and practice; the language of which is,
saying, This [is] the way, walk ye in it; it directs to Christ the way, and who is the only way of life and salvation to be walked in by faith, and to all the lesser paths of duty and doctrine, which to walk in is both pleasant and profitable, and which is the right way; so the Targum paraphrases it,
"this is the right way;''
to which agree the comments of Aben Ezra, Jarchi, and Kimchi; though the Arabic and Syriac versions, following the Septuagint, represent them as the words of seducers, directing to a wrong way: but the words are a promise of being led right, and not a threatening of being led wrong:
when ye turn to the right hand, and when ye turn to the left; through ignorance or inadvertency, through the prevalence of corruption, or force of temptation; and as it is promised there should be such a voice, so they should have ears to hear, their ears erect to attend to what is said, to observe it, and act according to it.
e T. Bab. Megilla, fol. 32. 1.