Although the Bible was written by more than 40 different authors, spread out across 3 different continents, in three different languages, and over a span of 1,600 years, it all ultimately has one Author. This diverse array of prophets and Apostles were all inspired (2 Timothy 3:16-17) by the Holy Spirit (2 Peter 1:19-21) of one everlasting (Psalm 41:13), unchanging (Hebrews 13:8), unteachable (Romans 11:34) God.
This beautiful truth means that whatever you read in one part of the Bible will match up perfectly with any other part. Moses fits nicely with Peter. Joshua works in harmony with John. The Psalms are woven throughout the Gospels. The prophecies of the Old Testament are fulfilled in the New, the antitypes of the New Testament were foreshadowed by their respective types in the Old. The entire Bible is the work of the One Holy God, and He makes His purpose for it quite clear within it: "All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, that the man of God may be complete, thoroughly equipped for every good work." (2 Timothy 3:16-17).
One of the most important doctrines in the entire Bible has, in the modern day, become known as "Sola Fide". In effect, Sola Fide (which literally translates to "faith alone") can be summed up as the belief that "...by grace you have been saved through faith, and that not of yourselves; it is the gift of God, not of works, lest anyone should boast. For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand that we should walk in them." (Ephesians 2:8-10).
A helpful proof that this doctrine is true is that not only can it be summed up in just a few Bible verses, but that it has a lot more than just a few Bible verses to defend it. Of course, we could play silly games and point out the large number of Church "Fathers" who preached Sola Fide. For example, in In Evangelium Matthaei Commentarius, the so-called "Hammer of the Arians", Saint Hillary of Potiers (315-368 A.D.), wrote "...fides enim sola justificat." ("Faith Alone Justifies"). But I find it unhelpful to appeal to the Church "Fathers", as if they were some kind of authority.
In truth, the Bible is the only authority a Christian will ever need to appeal to. It may, especially if one is dealing with a heretic, be useful to temporarily appeal to an authority they trust, but even this should be done with the intention to drag them back to the Bible. Thus, it is vital to show that the Bible itself teaches Sola Fide, not only in Ephesians, but right the way through Scripture, in both Old and New Testaments.
"Not so!" saith the Gospel deniers. See, there is only one place in Scripture where the words "faith alone" actually appear. In James 2:24, we read "You see then that a man is justified by works, and not by faith only." Nowhere else in the Bible do with find the words "faith alone". Thus, heretics argue, there is some major flaw in the belief that we are saved by faith alone. Namely, the only place in the entire Bible that talks about faith alone says we are not justified by faith alone.
But this line of reasoning is majorly flawed, beginning with this strange appeal to the exact words criteria. The exact words criteria is the bane of any literate person's existence. For one thing, it is usually a double-ended sword. My position (e.g. "God is Triune") may not be in Scripture explicitly. However, the Bible also does not say "God is not Triune". Thus, both sides must appeal to deductive reasoning. I can therefore say that, since the Bible says there is only one God, yet it identifies 3 distinct and coequal beings as God, God must be Triune. The only other conclusions are that there are three gods, and the Bible lied about there being one, or it lied about the Son and the Holy Spirit being God. Of course, although it's a terrible position, you can say that one Scripture or another is wrong. It is far more respectable to deny the truth, than the existence, of the written word. Nevertheless, if you believe, as all Christians do, that the Bible is the infallible word of the Living God, you cannot afford to deny its teachings, however they are phrased.
This means you simply cannot deny Sola Fide simply because there are no verses in the Bible that explicitly say "faith alone justifies", or "we are saved by faith alone", or "you do not need works to be saved" etc. This is because the Bible does say "Now to him that worketh is the reward not reckoned of grace, but of debt. But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness." (Romans 4:4-5). It does say "For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast." (Ephesians 2:8-10). It does say "And if by grace, then is it no more of works: otherwise grace is no more grace." (Romans 11:6). You could fill a book as long as the Psalms just listing Scriptures which clearly teach the doctrine of Sola Fide. Salvation is explicitly said to be received by grace, through faith, and not of works. Quite frankly, the only way God could make Sola Fide more clear in His word is if He, knowing ahead of time the arguments that heretics would come up with against His word, decided to include in it the exact words heretics are looking for.
But Gospel deniers will say they actually have a stronger case than anti-Trinitarians (if, indeed, they have the integrity to acknowledge the Trinity). See, although there are no verses that say "God is not Triune", we have already seen where James tells us a man is not justified by faith alone.
However, as we have already established, Scripture is internally consistent. It all comes from the same God, and as a result, it all teaches the same thing. Therefore, if Paul teaches that we are saved by grace, through faith, and not of works, James will not contradict him and say "actually, we are saved by works, and not by faith alone."
Now, if James was the only book in the Bible, or at least the only one that dealt with salvation, the necessity of works in salvation would be a feasible interpretation. However, not only is James not the only relevant book in Scripture, it is not even the only book referenced in James 2! In reality, whereas heretics will selectively quote the most convenient verses from James 2, the whole of the book quite clearly speaks not of doing works to get saved, but of doing works to prove our salvation. "What does it profit, my brethren, if someone says he has faith but does not have works? Can faith save him?" (James 2:14, emphasis added). "But someone will say, “You have faith, and I have works.” Show me your faith without your works, and I will show you my faith by my works." (James 2:18, emphasis added). "Was not Abraham our father justified by works when he offered Isaac his son on the altar? Do you see that faith was working together with his works, and by works faith was made perfect? And the Scripture was fulfilled which says, “Abraham believed God, and it was accounted to him for righteousness.” And he was called the friend of God." (James 2:21-23, emphasis added).
And so even if we completely remove James from the rest of Scripture and just read it in ignorance, already we see just how plausible the Sola Fide interpretation is. In full context, especially if you do the smart thing and follow James' references to Abraham, it's clear that James is saying true faith will produce works. Thus, he is talking about consistency. If you believe there is a God, you are going to act like there is a God. If you act like there is no God, how are you distinct from the fools who say there is no God (Psalm 14:1)?
But all this does is leave us with two competing interpretations: One that says we are saved by grace, through faith, and not of works, but that true faith proves itself by works, and another that says faith alone cannot save, and must be accompanied by works. And if James 2 was truly the only book in the Bible, these interpretations would be equal. But praise be to God, it is not alone.
As I have already pointed out, Sola Fide is so clearly presented in Scripture that it may be easily defined by citing just three simple verses. Or, technically, just two. Ephesians 2:8-9 is sufficient to establish that we are saved by grace, through faith, and not of works, because it explicitly says we are saved by grace, through faith, and not of works. The reason I like to include verse 10 is because it cuts off a common objection: "Shall we continue to sin that grace may abound?" (Romans 6:1). And it does so in a similar way to James 2! See, if "...we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand that we should walk in them", then salvation by grace, through faith, and not of works, is not an excuse not to have good works!
Just. Like. James. Says.
And so we see that James and Paul work in perfect harmony. But only if you take the Sola Fide position. If you reject Sola Fide, you will have a hard time explaining why Paul says salvation is not of works, yet James, in your view, says works are required. Paul contradicts James, and James contradicts Paul, so you will have a far harder time resolving this apparent contradiction than any Christian will ever have explaining why James 2:24 actually fits the Sola Fide position quite nicely.
Whenever you read an attack on Sola Fide, it will include, and likely rest upon, this obvious misinterpretation of James 2:24. Not that there are no other verses that are misquoted. Matthew 7:21, for example, is a popular target for such heretics. Philippians 2:12 is not entirely uncommon, either. But which is more likely? That Christians for the past 2,000 years have misunderstood the entire Bible, or that heretics have misrepresented 3 or 4 verses? Simple logic dictates that, given the sheer volume of Scriptures that militate against works-based "gospels", any interpretation that adds works to faith is invalid, and can be dismissed immediately. Let us therefore conclude with these beautiful words of Scripture:
"But what does it say? “The word is near you, in your mouth and in your heart” (that is, the word of faith which we preach): that if you confess with your mouth the Lord Jesus and believe in your heart that God has raised Him from the dead, you will be saved. For with the heart one believes unto righteousness, and with the mouth confession is made unto salvation. For the Scripture says, “Whoever believes on Him will not be put to shame. For there is no distinction between Jew and Greek, for the same Lord over all is rich to all who call upon Him. For “whoever calls on the name of the Lord shall be saved.”" (Romans 10:8-13). And all of God's people said "Amen!"