Who is grafted in according to Romans 11—believers or the Gentile system?
According to Romans 11, the Gentile system is grafted in, not believers as such. The old, no-good olive tree represents the Gentiles being grafted into the beautiful original olive tree, Israel. Believers are certainly part of it, but the passage speaks of the whole Gentile system grafted into what was originally Israel.
Les teaches that the Gentiles are like an old, no-good olive tree that has been grafted into the beautiful original, which was Israel. He makes it plain that the ones grafted in are not the believers, although believers are certainly part of it; rather, the whole Gentile system has been grafted into that which was originally Israel. He connects this to Abraham and Genesis 12:3, where God promised that all families of the earth would be blessed through Abraham, a promise never abrogated. Until Paul went to the Gentiles, Israel enjoyed the fatness of the root of Abraham.