The remnant of Israelites described by Paul in Romans chapter 11 is an extremely small group of believers adhering to a pure Circumcision gospel. Those whom Paul calls "the rest" in this chapter are
the majority of Israelites who believe in a mixed, muddled, Satanic gospel that is neither Peter's nor Paul's. In Galatians, chapter one, Paul calls this so-called gospel "anathema." It is basically the Christian gospel. Many of "the rest," however, will be awakened spiritually during the Tribulation and will become pure heralds of the Circumcision gospel.
