Are you completely unaware of both of these?
Rom 16:25-26 (AKJV/PCE)
(16:25) Now to him that is of power to stablish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began, (16:26) But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for the obedience of faith:
This mystery was kept secret since the world began, BUT NOW is made manifest.
James knows nothing about this mystery and is writing purely from the perspective of the doctrines that were given to Israel through the fathers and the prophets.
The same goes for Peter:
Acts 3:21 (AKJV/PCE)
(3:21) Whom the heaven must receive until the times of restitution of all things, which God hath spoken by the mouth of all his holy prophets since the world began.
James knows nothing of a salvation by grace through faith without works, like Paul speaks about.