Can anyone explain this apparent discrepancy between the Greek and Hebrew versions of Isaiah 30:20-21?

Question

Isaiah 30:21, as translated from the Masoretic text (Hebrew), has been used times to say that God can show us where we need to go.

וְאָזְנֶ֙יךָ֙ תִּשְׁמַ֣עְנָה דָבָ֔ר מֵֽאַחֲרֶ֖יךָ לֵאמֹ֑ר זֶ֤ה הַדֶּ֙רֶךְ֙ לְכ֣וּ בֹ֔ו כִּ֥י תַאֲמִ֖ינוּ וְכִ֥י תַשְׂמְאִֽילוּ׃

KJV translation:

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.

The Septuagint (Greek) version, however, means that the voice is coming from someone, not God, misleading you.

καὶ τὰ ὦτά σου ἀκούσονται τοὺς λόγους τῶν ὀπίσω σε πλανησάντων οἱ λέγοντες αὕτη ἡ ὁδός πορευθῶμεν ἐν αὐτῇ εἴτε δεξιὰ εἴτε ἀριστερά

Brenton's translation:

and thine ears shall hear the words of them that went after thee to lead thee astray, who say, This [is] the way, let us walk in it, whether to the right or to the left.

What is the cause of this difference?

Answer 1

The Hebrew is "וְאָזְנֶ֙יךָ֙ תִּשְׁמַ֣עְנָה דָבָ֔ר מֵֽאַחֲרֶ֖יךָ" – "your ears will hear a thing/word from behind you".

The Hebrew does not detail who is speaking in ones ear; while many traditional commentaries understand the speaker in ones ear to be God or His messengers (see Rashi, Radak), it is still possible to understand the speaker to be a trickster trying to lead one astray, as explained by the Septuagint.

Thus, it seems that while the Septuagint is adding an explanation to the Hebrew, the explanation is certainly a viable interpretation of the Hebrew.

Answer 2

The Hebrew translation is probably more accurate as the word Moreh is used for "Teacher" in relation to the word being heard for instruction. This Hebrew word uses the same root as the word "Torah". The idea of righteous action is further emphasized in the passage when it says we will "Shamah" (listen to) the instruction and "halakhah" (walk) in it. These are traditional Jewish terms, when put together, to indicate righteous behavior. This is emphasized even further by the colloquialism "neither to the right or to the left" indicating a path of righteousness in Jewish thought.