What Paul sees in "Justification" is of God while James based on the context sees" Justification" is of man giving proof of his faith.
I have heard this more times than you know. However, this statement is usually said blindly or parroted without any real good evidence from the context. The only case one will use is James 2:18. But this verse is not saying he is justified before men alone and not God. He is merely illustrating the point of example of his own life. He can equally be referring to being justified before God by his statement in James 2:18. In fact, we know James is talking about being justified before God. How do we know?
Looking at just James:
#1. You have to receive the engrafted words of the New Covent, which is able to save your souls. “…lay apart all filthiness and superfluity of naughtiness, and receive with meekness the engrafted word, which is able to save your souls.” (James 1:21).
#2. Like being a doer of the Word. However, the person who just hears the Word only deceives themselves. “ …be ye doers of the word, and not hearers only, deceiving your own selves.” (James 1:22).
#3. This includes having a pure religion undefiled before God in loving the fatherless and the widows in visiting them in their affliction and remaining unspotted from the world (Which are actions or works). “Pure religion and undefiled before God and the Father is this, To visit the fatherless and widows in their affliction, and to keep himself unspotted from the world.” (James 1:27).
#4. James then mentions a situation among the brethren whereby they showed “respect of persons” by giving favor to the rich brethren and not the poor brethren. This is sin. “But if ye have respect to persons, ye commit sin, and are convinced of the law as transgressors.” (James 2:9).
#5. And it leads to having judgment without mercy who showed no mercy. “For he shall have judgment without mercy, that hath shewed no mercy; and mercy rejoiceth against judgment.” (James 2:13).
#6. James 2:14-16 (KJB) says, “What doth it profit, my brethren, though a man say he hath faith, and have not works? can faith save him? If a brother or sister be naked, and destitute of daily food, And one of you say unto them, Depart in peace, be ye warmed and filled; notwithstanding ye give them not those things which are needful to the body; what doth it profit?” We see here another parallel of not having “respect of persons” in James 1:1-13 with James 2:14-16. It asks the question, “Can faith save him?” This is in view of not providing for your brother if they are naked or they do not have any food. We learn in 1 Timothy 5:8 that it says, “But if any provide not for his own, and specially for those of his own house, he hath denied the faith, and is worse than an infidel.” 1 John 3:10 says, “In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.”
#7. James 2:14-16 is the context to James 2:17 in that faith without works is dead. So this is an example of showing how it is a salvation issue involving one’s right standing with God. Well, that is if you believe the context. But many who hold to Unconditional Eternal Security will of course try to explain away the context because it does not fit their OSAS belief. They attempt to try and come up with a work around and cram new meaning into the Bible (eisegesis), and they will not let the text speak for itself (exegesis).