Author of James
James, a servant of God and of the Lord Jesus Christ, To the twelve tribes in the Dispersion: Greetings.
-- James 1:1 (ESV)
He does not state that he was James, the brother of the Christ or James the apostle. He was simply "a servant".
The Catholicism of Martin Luther’s time was hyper-focused on the value of works, but Luther found that Scripture repeatedly asserts we are saved through faith in Jesus Christ, not by anything we do. And yet the Book of James says that faith without works is dead (James 2:26). So what are we supposed to do with that? Was Luther wrong—do we need works to be saved? Or is James contradicting Peter and other important passages about the Christian faith?
The reality is that James is not suggesting in any way that works lead to our salvation. It’s a result of it.
Jesus uses the metaphor of trees and fruit to capture a similar idea. If we claim to have faith in Jesus Christ but our lives bear no evidence of that, it’s like claiming to have his good fruit, but all we produce is rotten. And he makes it clear what happens to trees with rotten fruit:
“By their fruits you will know them. Do people pick grapes from thorn bushes, or figs from thistles? Just so, every good tree bears good fruit, and a rotten tree bears bad fruit. A good tree cannot bear bad fruit, nor can a rotten tree bear good fruit. Every tree that does not bear good fruit will be cut down and thrown into the fire. So by their fruits you will know them. Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but only the one who does the will of my Father in heaven. Many will say to me on that day, ‘Lord, Lord, did we not prophesy in your name? Did we not drive out demons in your name? Did we not do mighty deeds in your name?’ Then I will declare to them solemnly, ‘I never knew you. Depart from me, you evildoers’” —Matthew 7:16–23
Martin Luther called the church to renew its focus on Christ, and as part of that he placed greater emphasis on books of the Bible that most magnified the glory of Christ. This is why Luther had strong reservations about James’ inclusion in the biblical canon, but that’s also exactly why it’s stayed there for centuries: James constantly echoes Christ’s own words and teachings.