2:19 there is one God. James is writing primarily to Jews, whose main religious distinctive was monotheism, as opposed to the pantheistic polytheism that characterized all the pagan religions of the day. Even now, there are only three monotheistic religions (orthodox Judaism, orthodox Islam and orthodox Christianity); all others are, to one degree or another, structured around evolutionary pantheism, and nowhere in Scripture is such pagan belief commended, or even condoned. In this verse, monotheism is commended by James, but even that is not sufficient to save. Only true Christianity acknowledges that the Creator must also be the Redeemer.
2:20 faith without works is dead. Many people have alleged that James was arguing here against Paul’s doctrine of salvation strictly by grace through faith. This idea is clearly wrong, however, because James wrote his epistle before any of Paul’s were written. Actually, there is no conflict between the two. James certainly taught that the works of the law could not save (note James 2:10; 4:17), and Paul taught clearly that genuine faith would produce good works (Ephesians 2:8-10). It is simply a semantic matter of emphasis. Salvation must be of grace, accepted by faith, since no one can earn it, but only God can know the heart and the reality of a profession of faith. But the reality of that faith can only be demonstrated to others by good works.