James 2:24 has to be the most misunderstood verse in the Bible. Works salvationists misinterpret it to mean that we are saved by works. In the first place, James is not using the word "justified" to mean "accounted as righteous" but is "shown to be righteous." James is discussing the proof of faith (says-claims to have faith but has no works/I will show you my faith by my works - James 2:14-18), not the initial act of being accounted as righteous with God (Romans 4:2-3). Works bear out the justification that already came by faith. In James 2:14, we read of one who says-claims he has faith but has no works (to back up his claim). This is not genuine faith, but a bare profession of faith. So when James asks, "Can that faith save him?" He is saying nothing against genuine faith, but only against an empty profession of faith/dead faith. So James does not teach that we are saved by works. His concern is to show the reality of the faith professed by the individual (James 2:18) and demonstrate that the faith claimed (James 2:14) by the individual is genuine. Simple!
In James 2:21, notice closely that James does not say that Abraham's work of offering up Isaac resulted in God accounting Abraham as righteous. The accounting of Abraham's faith as righteousness was made in Genesis 15:6, many years before his work of offering up Isaac recorded in Genesis 22. The work of Abraham was essential, not because it had some kind of intrinsic merit to save him, but because it proved or manifested the genuineness of his faith. Romans 4:2 - "For if Abraham was justified by works, he has something to boast about, but not before God" 4 For what does the Scripture say? "Abraham believed God, and it (faith, not works) was accounted to him for righteousness." Paul and James do not contradict each other. They are just explaining saving faith from two different perspectives. The harmony of Romans 4:2-3 and James 2:21,24 is seen in the differing ways that Paul and James use the term "justified." Paul, when he uses the term, refers to the legal (judicial) act of God by which He accounts the sinner as righteous. James, however is using the term to describe those who would prove the genuineness of their faith by the works that they do.
In the Strong's Exhaustive Concordance of the Bible, the Greek word for justified "dikaioo" #1344 is:
1. to render righteous or such he ought to be
2. to show, exhibit, evince, one to be righteous, such as he is and wishes himself to be considered
3. to declare, pronounce, one to be just, righteous, or such as he ought to be
God is said to have been justified by those who were baptized by John the Baptist (Luke 7:29). This act pronounced or declared God to be righteous. It did not make him righteous. The basis or ground for the pronouncement was the fact that God IS righteous. Notice that the NIV reads, "acknowledged that God's way was right.." The ESV reads, "they declared God just.." This is the sense in which God was justified, "shown to be righteous" not accounted as righteous.
Matthew 11:19 "The Son of Man came eating and drinking, and they say, 'Behold, a gluttonous man and a drunkard, a friend of tax-gatherers and sinners!' Yet wisdom is justified/vindicated/shown to be right by her deeds."
Man is saved through faith and not by works (Ephesians 2:8,9; Titus 3:5; 2 Timothy 1:9); yet genuine faith is vindicated, substantiated, evidenced by works (James 2:14-24). The word "alone" in regards to salvation through faith "in Christ alone" conveys the message that Christ saves us through faith based on the merits of His finished work of redemption "alone" and not on the merits of our works. It is through faith "in Christ alone" (and not by the merits of our works) that we are justified on account of Christ (Romans 3:24; 5:1); yet the faith that justifies is never alone (solitary, unfruitful, barren) if it is genuine (James 2:14-24). *Perfect Harmony.*