It's an epistle to the saints at Rome. They are gentiles.
They were a Messianic Believers Community. Your understanding is incorrect.
shalom b'SHEM Yah'shua HaMashiach
The strongest claim that one can make is that these saints at Rome consisted both of Jews of the flesh and gentiles. I'm sure there arose jealousies and false pride due to some "Jews" claiming special status because of their flesh. Paul would have none of it.
26* For ye are all the children of God by faith in Christ Jesus. 27* For as many of you as have been baptized into Christ have put on Christ. 28* There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus. 29* And if ye be Christ’s, then are ye Abraham’s seed, and heirs according to the promise. (Galatians 3:26-29)
The flesh means nothing. That which is born of the flesh is flesh. But that born of the spirit is spirit. This has always been true. (Jesus chided Nicodemus for not knowing this. (John 3:10)). Paul uses an allegory to explain what the effective force of the promise is, eliminating "flesh" as a variable in this salvific relation, if you will. (Sorry, I'm a math major).
22* For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman. 23* But he who was of the bondwoman was born after the flesh; but he of the freewoman was by promise. 24* Which things are an allegory: for these are the two covenants; the one from the mount Sinai, which gendereth to bondage, which is Agar. 25* For this Agar is mount Sinai in Arabia, and answereth to Jerusalem which now is, and is in bondage with her children. 26* But Jerusalem which is above is free, which is the mother of us all. 27* For it is written, Rejoice, thou barren that bearest not; break forth and cry, thou that travailest not: for the desolate hath many more children than she which hath an husband. 28* Now we, brethren, as Isaac was, are the children of promise. 29* But as then he that was born after the flesh persecuted him that was born after the Spirit, even so it is now. 30* Nevertheless what saith the scripture? Cast out the bondwoman and her son: for the son of the bondwoman shall not be heir with the son of the freewoman. 31* So then, brethren, we are not children of the bondwoman, but of the free.(Galatians 3:22-31)
This is an allegory. Both Ishmael and Isaac were "children of the flesh", but only one was the child of promise. Why? The passage explains it: pride in physical descent in lieu of faith is bondage. But faith in the promised seed (Jesus Christ--see Galatians 3:16) is freedom. Paul says in Romans 9:6 that "not all Israel is of Israel." The true Israel should not be confused with the Israel of the flesh. The commonwealth of Israel consists only those who are children of God by faith in Christ Jesus.
12* 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: 13* But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ. 14* ¶ For he is our peace, who hath made both one, and hath broken down the middle wall of partition between us; 15* Having abolished in his flesh the enmity, even the law of commandments contained in ordinances; for to make in himself of twain one new man, so making peace; 16* And that he might reconcile both unto God in one body by the cross, having slain the enmity thereby: 17* And came and preached peace to you which were afar off, and to them that were nigh. 18* For through him we both have access by one Spirit unto the Father. 19* Now therefore ye are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God; 20* And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone; 21* In whom all the building fitly framed together groweth unto an holy temple in the Lord: 22* In whom ye also are builded together for an habitation of God through the Spirit. (Ephesians 2:12-22)
Christ has broken down the middle wall of partition. We are no more strangers, but fellowcitizens with the saints. The saints.
(You wrote): Your understanding is incorrect. They were a Messianic Believers Community.
"Now I would not have you ignorant, brethren, that oftentimes I purposed to come unto you, (but was let hitherto,) that I might have some fruit among you also, even as among other Gentiles." (Romans 1:13)
They were predominantly gentiles, or else he would not have written "other" gentiles.