It was God that separated out the Jewish people....

"Turn to Leviticus 20: 24
Here we see the beginning of separation and by whom they were seperated  out.

24 But I have said unto you, Ye shall inherit their land, and I will give it unto you to possess it, a land that floweth with milk and honey: I am the Lord your God, which have separated you from other people.

Add to that verse 26 of the same book and chapter,

26 And ye shall be holy unto me: for I the Lord am holy, and have severed you from other people, that ye should be mine.

So the scripture bears out, the separation began with God.

Now the thought of that is maintained all through the scriptures until you come into the "body of Christ" revealed as a mystery by Paul. It was started by God and finished by God. 

Look at Exodus 33:16

16 For wherein shall it be known here that I and thy people have found grace in thy sight? is it not in that thou goest with us? so shall we be separated, I and thy people, from all the people that are upon the face of the earth.

So the separation of the Jewish and Gentile peoples are laid out by God.  Why do people have trouble understanding the truth as it is laid out in the scriptures. 

To the Jew first.....more later