The authenticity of James' letter is contested.
Some scholars see it as an anti-Pauline tract written around 80-90C.E. Also, they assert it is inspired from the Wisdom literature of the O.T. Apocrypha, in particular Hobit 4:5-19. But the differences in style & themes and the few analogies (such as charity for the poor) make the later claim very debatable.
Others (and myself) think that a large part of the epistle contains a rendition of Jesus' brother homilies or/and exhortations: despite being written in excellent Greek, the letter is disorganized, with reoccurring tenets & themes, as like a collection of randomly placed "sayings".
It was likely put together by someone who heard (and admired) James, in order to be read among Jewish Christians outside Palestine (as in Syria). Because the letter mentions repeatedly the contemporaries of James will be alive when the Kingdom comes (with God's wrath and very soon!), a date of issue beyond 70C.E. (when most people in Jerusalem perished) does not make sense. Rather, a date of writing prior to, or soon after, James' death is probable.
Also, in the epistle, God himself is the Judge of the coming Day (4:12, 5:7-11). This is typical of early Christian writings, as Paul's letters (Ro 2:3, 5-6, 5:16, 14:10b,12) and 'Hebrews' (12:23). However in later ones, written around 85-100 C.E, gMatthew (25:31-46), gJohn (5:25-30) and 'Acts' (10:42), Jesus has become that Judge.
Now, let's start by the passages the most likely to be authentic:
Jas 1:9-11 "Let the lowly
brother glory in his exaltation, but
the rich in his humiliation,
because as a flower of the field he will pass away. For no sooner has
the sun risen with a burning heat than it withers the grass; its
flower falls, and its beautiful appearance perishes. So the
rich man also will fade away in his
Jas 2:2-6 "For if there should come into your assembly a man with gold rings, in fine apparel, and there should also come in a poor man in filthy clothes, and you pay attention to the one wearing the fine clothes and say to him, "You sit here in a good place," and say to the poor man, "You stand there," or, "Sit here at my footstool," have you not shown partiality among yourselves, and become judges with evil thoughts?
Listen, my beloved brethren: has God not chosen the poor of this world to be rich in faith and heirs of the kingdom which He promised to those who love Him?
[quintessential belief of Jesus and the "Nazarenes". Let's also notice the present tense in "love", in contrast of the past tense in "promised": the "Nazarenes" must have believed Jesus had been "the apostle" (Heb 3:1) of God, revealing in his behalf, salvation (admission in the Kingdom) for the poor of his generation ("the door of Jesus": see later on). Let's also observe the Kingdom is to arrive when these poor (and also the wealthy ones, as shown later) are still alive. Also of interest: being poor is not enough to get in the Kingdom, you have to love God also (piety)]
` But you have dishonoured the poor man. Do not the rich oppress you and drag you into the courts?"
Jas 2:15-16 "If
a brother or sister is naked and destitute of daily food, and
one of you says to them, "Depart in peace, be warmed and
filled," but you do not give
them the things which are needed for the body,
what does it profit?"
Jas 5:1-5 "Come now,
you rich, weep and howl for your
miseries that are coming upon you!
[allusion to the "negatives" to be administered when the Kingdom arrives]
` Your riches are corrupted, and your garments are moth-eaten. Your gold and silver are corroded, and their corrosion will be a witness against you and will eat your flesh like fire [see 3:6b]. You have heaped up treasure in the last days.
[it was thought the Kingdom would arrive very soon and before these wealthy ones die!]
` Look! The wages you failed to pay the workmen who mowed your fields are crying against you. The cries of the harvesters have reached the ears of the Lord Almighty.
[no mention of Jesus in heaven (here and in the whole letter!). However, as can be gathered in Eusebius' "the History of the Church" 2, 23, quoting Hegesippus (a Christian), James (described here as the ultimate holiest Jew) used often his brother's name in the simple expression: "the door of Jesus" (meaning salvation but without any elaboration)]
` You have lived on earth in luxury and self-indulgence. You have fattened yourselves in the day of slaughter.
[allusion to the "day of the Lord (God)" and his judgment: see later]"
Also of interest and with a high likelihood of authenticity, in
the same letter: 1:2-8, 12-15, 19-27; 2:7-14, 17-26; 3:1-18; 4:1-12,
James believed that "faith without deeds is dead" (2:26 also 2:14,20) and exhorted for deeds (see Gal 2:10): "Religion that God our Father accepts as pure and faultless is this: to look after orphans and widows in their distress and to keep oneself from being polluted by the world." (2:27).
He warned about "great boasts" (3:5) (see Paul in 2 Cor 10:13-14, 11:10, 16-18,21, 12:1,5,6) and slips of "the tongue" ("a restless evil full of deadly poison" 3:8) from "teachers" causing disaster in one's life (3:1-6).
The royal law is mentioned "Love your neighbour as yourself" (2:8) but warned that "friendship with the world is hatred toward God" (4:4, also in 1:27; see Gal 2:12-13, 1 Cor 2:12,11:32, 2 Cor 6:14,7:10).
For him, the Law (of Moses) is "the perfect law that gives freedom" (1:25 also in 2:12. But Paul wrote in Gal 3:10a "All who rely on observing the law are under a curse")
and "For whoever keeps the whole law and yet stumbles at just one point is guilty of breaking all of it." (2:10)
"The prayer offered in faith [especially from righteous elders (5:14,16)] will make the sick person well" (also in Mk 9:29). Anointing with oil is also recommended for the sick (also in Mk 6:13). Sins can cause illness (5:13-16), even death (1:15b, 5:20). Big sinners should "grieve, mourn and wail ... Humble yourselves before the Lord [God], and he will lift you up" (4:9-10)
God (the Lord) is the "Law-giver and Judge". (4:12, 5:9), "able to save and destroy" (4:12) at Judgment Day (5:9) and the Lord (Job's God, 5:11) is coming soon (5:7-8) and "the Judge is standing at the doors" (5:9). But "The Lord is full of compassion and mercy" (5:11) and "Mercy triumphs over judgment!" (2:13). See next note:
In the letter, James appears to have been a responsible (and sympathetic) leader projecting authority and popular wisdom. He was concerned by the (spiritual and physical) welfare of his community (and possibly others). And he was not scheming about doctrine, theology (like Paul) and rituals.
Finally, James' letter has so little Christianization added ("Lord
Jesus Christ" (1:1) and "glorious
Lord Jesus Christ" (2:1): that's it), so much conservative
(non-hellenistic) Judaism, and, on some points, conflicting with
Christian doctrines, that it barely made it into the New Testament.
Note: "... the New [Testament] has its deuterocanonical books ..., their canonicity having formerly been a subject of some controversy in the Church. These are for the entire books: the Epistle ... of James ..." (Catholic Encyclopedia: Canon of the New Testament)
And the imagery complementing unequivocally the plain language is very reminiscent of Jesus' sayings, even if James' homilies or/and messages appear more sophisticated.
But let's notice NO parable, NO Jesus as a teacher, NO
"sacrifice", NO Jesus in heaven, NO future resurrections,
NO Son of God, essentially reflecting James was not a Christian as confirmed here