I think that this change from the Hebrew perfect to the Greek future represents a shift in theology, or at least a shift in the way the Jews saw themselves, in a post-586/7 BC world. The Jews had to rethink what had happened and why they went into exile. I think that one of the things that came out of that exile is the need to seek and achieve righteousness and holiness as the primary focus for the Jew. Then based upon their faithfulness to Yahweh (Kurios), they would be accepted by God.

I think that is also why torah became nomos in the LXX. Torah was a term that meant instruction and was in the context of a relationship that was established. Nomos is law, cold law, that came from western society. Instead of the Torah being God’s instructions to those he was in covenant with, it became nomos and those who failed to follow nomos died and those who were faithful and obedient to nomos lived.

But this is speculation at best on my part for right now. I would like to look into this more when I get the opportunity.

I wonder why the Greek is so drastically different here; I mean this is pivotal to ones theology I would imagine.