James gives us a backwards (=biblical) view of money here.
A biblical view of money leads one to the conclusion that wealth is ultimately cancerous to our souls. Why? Because it slowly deceives us, day by day, into placing too much hope in money. Jesus warned of a rich fool in Luke, who said this: “I will say to my soul, Soul, you have ample goods laid up for many years; relax, eat, drink, be merry” (Luke 12:19). God responds to him and says “You fool!”
Wealth is not wicked in itself and poverty is not virtuous in itself. But both lead to certain predispositions that bear themselves out in our faith. That is why the poor are rich in faith; they are generally more physically and tangibly aware of their utter dependence on God day by day.
Since I receive my living from financial support, I have heard this sentiment many times from others: “I could never do what you do, living on faith for each paycheck.” But those are the sentiments of middle-class spirituality; the idea that only a select few depend on God for their living.
The reality is, God is more generous than any boss or CEO, more wealthy than a fortune 500 company, and only he is truly concerned with our well-being. Those who are poor understand this well; they are on the short end of the stick most of the time. They have no recourse but to trust in God. Thus, James says that those people in that position are spiritually wealthy.