In which Paul seems to misquote the old testament in order to change it's meaning.
So that you may not claim to be wiser than you are, brothers and sisters, I want you to understand this mystery: a hardening has come upon part of Israel, until the full number of the Gentiles has come in.
26 And so all Israel will be saved; as it is written, “Out of Zion will come the Deliverer; he will banish ungodliness from Jacob. And this is my covenant with them, when I take away their sins.” Romans 11:26-27
20 And he will come to Zion as Redeemer, to those in Jacob who turn from transgression, says the Lord.
21 And as for me, this is my covenant with them, says the Lord: my spirit that is upon you, and my words that I have put in your mouth, shall not depart out of your mouth, or out of the mouths of your children, or out of the mouths of your children’s children, says the Lord, from now on and forever.
There are several disturbing things about this passage. First, it should be clear that in Isaiah, God says he will keep his promise to those in Jacob who turn away from their transgressions. But in Paul, God says he will remove ungodliness from Jacob. The actor has changed away from a person's personal responsibility to repent and return to God, into something that God is going to do. In particular, he is going to “banish” them. Paul makes his message clear in the line following this when he says “28 As regards the gospel they are enemies of God for your sake… 30 Just as you were once disobedient to God but have now received mercy because of their disobedience, 31 so they have now been disobedient in order that, by the mercy shown to you, they too may now receive mercy. 32 For God has imprisoned all in disobedience so that he may be merciful to all.”
What Paul is saying is clear. Israel, the Jews, are no longer a light to the Gentile nations. In fact, the Gentile nations (who believe in Jesus and worship him) are now the light to Israel. This is a 180 degree difference than the eternal covenant mentioned in Isaiah 59:20-21.
Paul reinforces the idea above with his next line, “And this is my covenant with them, when I take away their sins”. The only problem is, this isn't what the second verse says in Isaiah, and it isn't a small change either. It's not even a paraphrase. Paul just removed the part when God says he will put his law into their mouths forever and ever, and replaced it with a completely different theology – that God would take away their sins. Of course in doing so he also removes the statement that God's covenant with Israel was an eternal covenant (“from now on and forever”).
Obviously the idea behind what is being said in Isaiah is anathema to Paul's Christian theology that God has rejected Israel as a light to the nations, and that all Gentile nations must now accept Jesus as their savior. The idea that God's covenant with Israel is that his word will never leave their mouth forever does not comport with the idea that their purpose has been removed, the plan has been changed and they now need to accept and pray to Jesus. But in saying so, Paul appears to have twisted the old testament scriptures in an effort to make us believe God said something he did not say.
The Christian response is that Paul was quoting from the Septuagint. However, if this is true, it only moves the problem away from Paul and onto the Septuagint. We would then need to understand why the Septuagint is so different than Isaiah in the original Hebrew. There are other secondary problems with this claim which impeach it as unacceptable. For example, we must ask why Paul, a “Pharisee of Pharisees” and a student of Gamaliel, the giant of his generation – would choose to use the Septuagint.
In Paul's day, he would have had access to the Hebrew of the Dead Sea Scrolls, which is word-for-word accurate (some spelling errors in some scrolls though) with the masoretic texts we have today. We can assume serious copies made by professional scribes would not contain gross errors such as spelling errors. Paul would have had access to these, especially as a student of Gamaliel. I say this to point out that we know the issue as we see it today was set before Paul.
Christians I have discussed this with on the internet have a tendency to dodge the main issue and give accusations of spiritual blindness. In one instance four active debaters refused to even admit that Paul was quoting Isaiah 59 at all. I was told by one Christian that if I read the rest of Romans I would “understand” what Paul was talking about. And so forth.
In any case, if any new information comes up which can explain why Paul's quote here seems to mean the exact opposite of what it says in Isaiah, I will be more than happy to include that information here!