Hi, Brother Ruben! At first Martin Luther raised that crazy idea for how recently he was converted, and that book hit his theology, the one he had been taught at home. Other theologians affirm that James is legalistic, nevertheless, this book was recognized within the canonical books and is well considered like divine inspiration, so that it would be badly to eliminate it. Martin later recognized him as canonical after discovering his spiritual wealth.

Thanks for the question brother, I hope my explanation is clear. regards