I think a mistake was made when the teaching became popular that the church is an entity entirely separate from Israel, the bible does not give us that picture at all. The church is the obedient of Israel to which was added the obedient of the gentiles, that is the way it started and the way it still is. There is a difference today between the ratio of Jews to gentiles, in the beginning the Jews outnumbered the gentiles but today the gentiles far outnumber the Jews. Even with that there are no doubt many more Jewish believers in Jesus Christ today then there was in the first century church. At the end of the age what is left of the nation of Israel will come into the fellowship of faith in Christ...they will come into the same body of Christ that is the church.
"At the end of the age what is left of the nation of Israel will come into the fellowship of faith in Christ"
Where is such teaching found in the New Testament? "Thus all Israel will be saved" is not it.