In the Greek Septuagint, Jeremiah 31:37 is literally translated as:
‘Thus says the/Lord:
If should/be/raised/up the sky in height,
And/if lowered the floor of/the land below,
I WILL/NOT reject the/race of/IsraEl, says the/Lord,’
For all/the/things that they’ve/done.’
However, the Hebrew Masoretic text reads differently (as translated):
‘Thus says the Lord: If the heavens above can be measured and the foundations of the earth searched out below; Then I WILL also cast off all the offspring of IsraEl for all that they have done, declares the Lord.’
As you can see, there is a significant difference between the two source texts! On the one hand, the Greek Septuagint says that IsraEl will not be rejected, but the Hebrew Masoretic text says that they will be cast off! Which is right?
The previous verse (36) seems to provide the answer. It says:
‘If these Laws before Me should cease to be,
Then the race of IsraEl will no longer stand
As a nation before Me
Throughout the rest of their days.’
So God is clearly saying that IsraEl could be rejected. The very next verse would hardly contradict what has just been spoken. Therefore, we have concluded that the Greek Septuagint text is in error in verse 37, and the Hebrew text is correct. Perhaps the Septuagint translator simply couldn’t believe that IsraEl might be rejected, and because of this, he added the negative word ‘not’ (ouk) to the sentence.
Does this mean that the Greek Septuagint is inferior to the Hebrew? No, not necessarily. We continually find obvious errors in both sources! However, most of the time the Greek Septuagint simply makes more sense, and even offers small details that are not found in the Hebrew versions. So, we tend to trust the Greek Septuagint text, while admitting that it is not perfect, and keeping an eye out for errors.
Besides, if someone wishes to read a Bible based on the Hebrew, there are many ones available, but very few based on the Greek.
To learn more about why we use the Greek Septuagint, please see this page.