There are three men called James in the New Testament: James the son of Zebedee (Mk1:19, Acts 12:2; etc.) who was one of the inner circle of apostles; James the son of Alphaeus, likely to be James the younger or ‘little James’ (Mk 3:18; 15:40) and James, son of Joseph and Mary, the Lord’s brother (Mt 13:55; Acts 12:17; 15:13ff; 1 Cor 15:7; Gal 1:19; 2:9).
As you can see from the references, James, the son of Joseph and Mary was a significant leader in the early church and was well acquainted with Paul’s work, which we see reflected in this letter. James the son of Zebedee was martyred in 44AD, James the son of Joseph and Mary was martyred in Jerusalem between 62-67AD. There were not many, after Paul had written his major letters, who could write a letter to the church everywhere (the twelve tribes of the dispersion 1:1) and simply sign it ‘James, a servant (lit. ‘Slave’) of God and of the Lord Jesus Christ.’
James’ letter sometimes reads like preaching notes, seeming to change topic quickly only to return to an earlier theme. In this way it reads like the wisdom literature of the Old Testament (Proverbs, Ecclesiastes, Song of Songs, some of the Psalms, Job and sections of other books) where the abrupt change in direction and the abrupt language is a foil designed to make us think hard and link the concepts that otherwise appear to be separate.