Yes, of course there are two groups. Jews and gentiles.
Eph 2:
11Therefore remember that formerly you, the
Gentiles in the flesh, who are called “Uncircumcision” by the so-called “Circumcision,” which is performed in the flesh by human hands—
12remember that you were at that time separate from Christ, excluded from the commonwealth of Israel, and strangers to the covenants of promise, having no hope and without God in the world.
13But now in Christ Jesus you who formerly were far off have been brought near by the blood of Christ.
14For He Himself is our peace, who made both
groups into one and broke down the barrier of the dividing wall,
15by abolishing in His flesh the enmity,
which is the Law of commandments
contained in ordinances,
so that in Himself He might make the two into one new man, thus establishing peace,
In my last post I cited Romans 2 because obviously that is very close to the context of the verse you first quoted in Romans 4. But I think it is clear from the whole of Paul's writings that he has a big thing about the rapprochement of Jews with Gentiles. At the time, Jews held an extremely condescending attitude towards non-Jews and Paul clearly made it his mission to overcome this prejudice. Of course outside the church they could do whatever they wanted, but within the church Paul was very intolerant of Jewish Christians who mistreated the gentile Christians. This is very much in evidence in Galatians where even Peter fell into the trap and had to be rebuked by Paul for refusing to share fellowship with gentile believers. Paul's conclusion? In Christ there is neither Jew nor Greek (another term for gentile) and then extending this to other possible areas of prejudice - male-female and slave-free. Christ made all men equal. Faith was a universal principle that transcended petty nationalistic or cultural or religious differences. Christ was not divided.