“1. Scripture alone. When the Reformers used the words sola Scriptura they were expressing their concern for the Bible’s authority, and what they meant is that the Bible alone is our ultimate authority—not the pope, not the church, not the traditions of the church or church councils, still less personal intimations or subjective feelings, but Scripture only. Other sources of authority may have an important role to play. Some are even established by God—such as the authority of church elders, the authority of the state, or the authority of parents over children. But Scripture alone is truly ultimate. Therefore, if any of these other authorities depart from Bible teaching, they are to be judged by the Bible and rejected.
2. Christ alone. The church of the Middle Ages spoke about Christ. A church that failed to do that could hardly claim to be Christian. But the medieval church had added many human achievements to Christ’s work, so that it was no longer possible to say that salvation was entirely by Christ and his atonement. This was the most basic of all heresies, as the Reformers rightly perceived. It was the work of God plus our own righteousness. The Reformation motto solus Christus was formed to repudiate this error. It affirmed that salvation has been accomplished once for all by the mediatorial work of the historical Jesus Christ alone. His sinless life and substitutionary atonement alone are sufficient for our justification, and any ‘gospel’ that fails to acknowledge that or denies it is a false gospel that will save no one.
3. Grace alone. The words sola gratia mean that human beings have no claim upon God. That is, God owes us nothing except just punishment for our many and very willful sins. Therefore, if he does save sinners, which he does in the case of some but not all, it is only because it pleases him to do it. Indeed, apart from this grace and the regenerating work of the Holy Spirit that flows from it, no one would be saved, since in our lost condition, human beings are not capable of winning, seeking out, or even cooperating with God’s grace. By insisting on ‘grace alone’ the Reformers were denying that human methods, techniques, or strategies in themselves could ever bring anyone to faith. It is grace alone expressed through the supernatural work of the Holy Spirit that brings us to Christ, releasing us from our bondage to sin and raising us from death to spiritual life.
4. Faith alone. The Reformers never tired of saying that ‘justification is by grace alone through faith alone because of Christ alone.’ When put into theological shorthand the doctrine was expressed as “justification by faith alone,” the article by which the church stands or falls, according to Martin Luther. The Reformers called justification by faith Christianity’s “material principle,” because it involves the very matter or substance of what a person must understand and believe to be saved. Justification is a declaration of God based on the work of Christ. It flows from God’s grace and it comes to the individual not by anything he or she might do but by ‘faith alone’ (sola fide). We may state the full doctrine as: Justification is the act of God by which he declares sinners to be righteous because of Christ alone, by grace alone, through faith alone.
5. Glory to God alone. Each of the great solas is summed up in the fifth Reformation motto: soli Deo gloria, meaning ‘to God alone be the glory.’ It is what the apostle Paul expressed in Romans 11:36 when he wrote, ‘to Him be the glory forever! Amen.’ These words follow naturally from the preceding words, “For from him and through him and to him are all things” (v. 36), since it is because all things really are from God, and to God, that we say, ‘to God alone be the glory.’”
–James Montgomery Boice, Whatever Happened to the Gospel of Grace? (Wheaton, Ill.: Crossway, 2001), pp. 65-149.
What follows below is a very short summary of what is known as the five solas (sola being the Latin word for "alone"). It comes from the book "Whatever Happened to the Gospel of Grace?" by Dr. James Montgomery Boice.
I cannot recommend this book highly enough. It is a wonderful biblical overview of something near and dear to the heart of God - the very gospel itself. I have read and re-read it many times and each time I do so, I am astonished at the clarity and impact it has on my heart and life. The message of the gospel thunders forth from each page. It presents a stirring challenge to the Church in our day to forsake the trivial and rediscover "the doctrines that shook the world."
I wish I could put this book in the hands of every Christian and that they would read it and live life in the beauty and power of Christ and His gospel of grace. - Pastor John Samson