Is the Body of Christ unique to the current age of grace?

Les explains that Ephesians 5 uses the husband and wife relationship on earth to correlate with Christ as the Head, or husband, and the Body of Christ, which is the composite of church age believers. He says he does not believe Old Testament believers will be members of the Body that is strictly part and parcel of Israel's relationship to her Jehovah God. The Body is that unique relationship especially of the Gentile, though it includes some Jewish people—but not many. There are Jewish members of the Body. However, the Body of Christ is unique to this age of grace, those who have come in by believing and trusting the finished work of the cross, or the gospel. Therefore, Old Testament believers are not in this language.