You do understand James wrote to the Church both Jew/Gentil, the twelve tribes scattered abroad as seen in James 1:1
The early church assemblies in "buildings" were assemblies in Jewish Synagogs, primarily established by (Tribesmen), all calling themselves Jews, (even as they do to this day).
"Jesus" began the teaching TO THE JEWS, of the TRIBE of JUDAH, first, OF THEIR CHRIST MESSIAH and thereafter sent out His Apostles to all the TRIBES.
The "Synagogs", did not Become THE CHURCH...
the men Already having BELIEF IN GOD...who "assembled"
* Having Converted in Acceptance of Jesus their Christ Messiah, BECAME "The CHURCH", AND THEY being CALLED "Brethren", of God believing Jews, who ALSO Converted and ACCEPTED Jesus as their CHRIST MESSIAH.
THAT ^ is who James was "addressing" in his Letter as HIS BRETHREN.
Primarily JEWS, assembled IN Synagogs.
Gentiles DID NOT FLOCK to Synogogs, to HEAR of "the Heavenly God"...BEFORE Jesus arrived ON EARTH...
* Less you forget..."Gentiles" primarily were "believers in PAGAN gods... (men, moon, statues, whatever, were THEIR gods...without knowledge, of the Heavenly God and His Christ Messiah, of belief thereof." )
* James A Jew, already Believed IN GOD...
His Acceptance of Jesus the Christ Messiah, occured shortly after Jesus' Death and Resurrection, and James, becoming a Pillar of Preaching the SAME; Primarily TO JEWS, of God and His Chirst Messiah... JESUS.
* Pauls Commission, Followed, thereafter... Primarily Preaching to the Gentiles...
The Heavenly God,
and His Christ Messiah; JESUS.
* Early DAYS of the CHURCH...as now, IS NOT ABOUT THE "BUILDING"...but rather "ABOUT"...
An individual MAN
Heartfully Believing and Vow Committed
IN the Heavenly God and His Christ Messiah
* EARLY DAYS...were
a great Transition...
FOR Jews/ all Tribesmen ...
* ONE THING (accepting their Christ Messiah HAD ARRIVED)
AND
FOR Gentiles ... (accepting A DIFFERENT GOD
AND His Christ Messiah)...
* TWO THINGS
SURE, SOME Gentiles were hearing and following and a FEW committing... However, it was a SLOW transition...for Jews, (Tribesmen)...and SLOWER yet for Gentiles.
Consider...the "communication". A snails pace, by today's standards.
How quick would you be TODAY... to accept a Different "god", and "His Messiah"....if all you Heard, was a couple of "Jewish men, you did not know, come to town, and preach in the town square?
James was sending his Letter to the Synagogs, to be read (By deacons OF the Synagogs, accepting Jesus the Christ Messiah) to the assembly of men in the Synagogs, to the ears of Jews, Tribesmen, already themselves Accepting Jesus, as their Christ Messiah...as James called THEM;
His Brethren.
James Letters...were specific to his BRETHREN....YET, those in assembly NOT yet committed TO CHRIST, were being given ADVANTAGEOUS KNOWLEDGE, of what APPLIES to men WHO DID/DO accept Jesus as their Christ....and to PRESUME, the assembly in the Synagogs ... were over flowing with CONVERTED Gentiles... is a far stretch.
Considering...even Jesus' preaching in the streets, in the outer courts, in a field...
Both Jew and Gentiles that came to HEAR...
Were not "CONVERTS", but rather the "CURIOUS".... And many, Jews & Gentiles "ONLY HEARING", walked away IN REJECTION.