From 05/05/2004 on a previous blog:

But if some of the branches were broken off, and you, although a wild olive shoot, were grafted in among the others and now share in the nourishing root of the olive tree, do not be arrogant toward the branches. If you are, remember it is not you who support the root, but the root that supports you. Then you will say, “Branches were broken off so that I might be grafted in.” That is true. They were broken off because of their unbelief, but you stand fast through faith. So do not become proud, but stand in awe. For if God did not spare the natural branches, neither will he spare you. Note then the kindness and the severity of God: severity toward those who have fallen, but God’s kindness to you, provided you continue in his kindness. Otherwise you too will be cut off. And even they, if they do not continue in their unbelief, will be grafted in, for God has the power to graft them in again. For if you were cut from what is by nature a wild olive tree, and grafted, contrary to nature, into a cultivated olive tree, how much more will these, the natural branches, be grafted back into their own olive tree (Romans 11.17-24).

Paul says that the Gentiles now included in the Abrahamic Covenant can fall under the same judgment that the Jews fell under. Is there any way to interpret this passage so that it means, “Don’t you become merit legalists just like those Jews were all merit legalists”? No. What Paul says is that Gentiles must not become proud–arrogant toward another ethnic group, the Jews. Merit legalism is, of course, a form of pride. But that is simply not the direct object of this warning. I’m listening to John Piper preach on this passage and he quite clearly states that Paul is rejecting an attitude of ethnic superiority. So, since Paul is telling the Gentiles not to fall into the same sin as the Jews did, how can we say that Paul is dealing with merit legalism among the Jews throughout Romans? So on balance, Paul writes a letter which opposes the Gospel to something that the Jews are doing, arguing that God “is not the God of the Jews only,” but “of the Gentiles also.” He includes as a step in his argument that “God is one” and therefore could not be the exclusive property of Jews. He then ends a long argument warning believing Gentiles not to feel or act or think themselves superior the Jews on the basis of their election.