Commenting on the difference between Lev 20:5 in the Masoretic Hebrew Text and the LXX, Heath D. Derwell, in a very insightful volume on child sacrifice in the Ancient Near East, wrote:
Appearing at the conclusion of a relatively lengthy prohibition against offering one’s child למלך, the Masoretic Text of Lev 20:5 reads:
ושׂמתי אני את־פני באישׁ ההוא ובמשׁפחתו והכרתי אתו ואת כל־הזנים אחריו לזנות אחרי המלך מקרב עמם
And I myself will set my face against that man and against his family. I will cut him off and all who whore after him, by whoring after the Molek, from the midst of their people.
Buber and others are correct to note that the most natural reading here is to understand “Molek” as an idol or deity rather than as the name of a sacrifice could in fact be “whored after” and that this is simply the only instance in the Hebrew Bible. Significantly, however in precisely this spot an important but largely overlooked textual variant exists—one that may actually preserve a superior reading. Specifically, where the MT reads לזנות אחרי המלך “to whore after the Molek,” LXX has ὥστε ἐκπορνεύειν αὐτους εἰς τοὺς ἄρχοντας “their whoring away into the rulers.” The variant cannot be dismissed out of hand as simply a loose rendering, because LXX Leviticus generally presents a quite wooden translation, and although this translation philosophy often leads to a less aesthetically pleasant translation, it does have the benefit of enabling the modern textual critic to reconstruct LXX’s Hebrew Vorlage with relative confidence.
For this reason, establishing the probable Vorlage of ὥστε ἐκπορνεύειν αὐτους is fairly straightforward; ωστε + infinitive (+ accusative pronoun) is a standard way for LXX Leviticus to render Hebrew ל + infinitive (+ pronominal suffix). Thus, one would expect ὥστε ἐκπορνεύειν αὐτους to represent a Hebrew Vorlage לזנתם “for their whoring,” rather than MT לזנות “to whore.” This is not the only discrepancy. Even more significant is LXX εἰς τοὺς ἄρχοντας, which corresponds to MT אחריו לזנות. First, LX preserves a plural form rather than a singular one as in the MT, and there is no obvious reason for an LXX translator to have rendered the singular המלך with a plural form. Even more surprising, though, is the anomalous correspondence of MT אחרי to LXX εις. The normal way for the LXX of Leviticus (and the Old Greek translations of the Hebrew Bible in general) to render אחר/אחרי is with either μετα (sometimes followed by τουτο/ταυτα) or οπισω. Considering the matter from the other direction, when the LXX reads εις in Leviticus (and the OG in general), it typically translates Hebrew ל, אל, or ב, with a few exceptions. In no case other than Lev 20:5 does εις correspond to אחר/אחרי. Furthermore, when we broaden the scope of investigation to the Hebrew Bible in general, every other MT attestation of √זנה followed by אחרי has an OG correspondence in the form of (εκ)πορνευω + οπισω/οπισθεν. Significantly, one of these instances appears in Lev 20:6, immediately following our verse. Thus, if the LXX translator of 20:5 did have לזנות אחרי before him, he chose to translate the phrase differently from one verse to the next. In sum, the correspondence of MT לזנות אחרי המלך to LXX ὥστε ἐκπορνεύειν αὐτους εἰς τοὺς ἄρχοντας is odd. It should thus come as no surprise that the recensions of Aquila, Symmachus, and Theodotion all exhibit discomfort with LXX and correct to οπισω του μολοχ, which unlike LXX does correspond nicely to the Hebrew of the Masoretic tradition. (Heath D. Dewrell, Child Sacrifice in Ancient Israel [Explorations in Ancient Near Eastern Civilizations 5; Winona Lake, Ind.: Eisenbrauns, 2017], 30-33)
