What you gotta understand is, is that these churches the epistles were writing to Romans Ephesians, Philippians, ,Colossians, Thessalonians etc.. were all scattered Israelites who lived amongst the gentiles and didn't know they were Jews. lets prove that by going into the scriptures.
zechariah 1:19 And I said unto the angel that talked with me, What be these? And he answered me, These are the horns which have scattered Judah, Israel, and Jerusalem.
Matthew 26:31 Then saith Jesus unto them, All ye shall be offended because of me this night: for it is written, I will smite the shepherd, and the sheep of the flock shall be scattered abroad
James 1:1 James, a servant of God and of the Lord Jesus Christ, to the twelve tribes which are scattered abroad, greeting.
The jews who were scattered into all nations were considered as gentiles or strangers because they didn't who they were and would take on the religions and customs of the heathen.
1 Peter 1:1Peter, an apostle of Jesus Christ, to the strangers scattered throughout Pontus, Galatia, Cappadocia, Asia, and Bithynia,
Ephessians 2:11 Wherefore remember, that ye being in time past Gentiles in the flesh, who are called Uncircumcision by that which is called the Circumcision in the flesh made by hands;[SUP]12[/SUP] That at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world:
1 Corinthians 12:2 Ye know that ye were Gentiles, carried away unto these dumb idols, even as ye were led.
do you see what I mean?