It is obvious that 'Christ Jesus' is an interpolation or insertion.
That there had been an outburst of persecution among the believers in Rome is also obvious. The religion of these folk had nothing to do with an imaginary Jesus. It had a Jewish origin among the prophets. It was routed in the spirit of God indwelling each individual from birth. I am convinced that the person being addressed was indeed Seneca who went into exile.
The spirit was thought to have passed down through mothers. I don't know who Seneca's grand mother and mother were but Seneca certainly wrote about them. The spirit sustained life. It could be fanned into 'flame'.
James's theology is heavily coloured by stoic ideas which would undoubtedly have appealed to Seneca. I think it went further than merely 'appealing', to believing what James taught about the spirit. The deaths of a number of people were linked to that persecution. I include the deaths of Nero, his wife Poppea, his mother Agrippina, Seneca, Burrus and Epaphroditus. I can only think that they were murdered by those opposed to the introduction of a Jewish prophetic religion with its indwelling of the spirit of God. The historians gave unbelievable, fabricated accounts of their deaths. This was a persecution of CHRISTIANOS, a latin name found at Pompeii visited by the elite Roman rulers. The CHRISTIANOS (anointed ones) were in fact called atheists because they didn't worship a physical god like an idol, but worshipped a spirit, as in Acts.
[You know very well in how many ways he helped me in Rome.]