Excerpted from a post on the First Presbyterian Jacksonville blog:

The Reformational churches were more faithful to Biblical authority and doctrine than the medieval Catholic Church.
Luther’s theology focused on the doctrine of justification by faith alone, which he called “the article of a standing or a falling Church.” He taught, contrary to Rome, that we are justified (accounted righteous before God) by the means of faith alone, apart from the works of the Law. Rome, on the other hand, taught that in justification we are “made righteous” via faith and obedience. Luther’s teaching was but a recovery of the Pauline doctrine of justification. Luther stressed imputed righteousness rather than infused righteousness. That is, God justifies sinners by crediting Christ’s righteousness to their account, not by implanting righteousness into them and thus justifying them. Our spiritual forefathers were willing to die for this distinction, for the Gospel was at stake.
This doctrine became known as Sola Fide “Faith alone” (justification by faith alone in Christ alone — not by faith and works). The other four points of what we might call the “Five Points of the Reformation” are: Sola Scriptura “Scripture alone” (the Scripture as the sole ultimate authority for Christian faith and practice — not the Pope, the Church, reason or feelings), Sola Gratia “Grace alone” (salvation by God’s grace alone, not human merit), and Solo Christo “Christ alone” (salvation by the mediation and merits of Christ alone, not the intercession of priests nor the merits of saints), and Soli Deo Gloria “to God alone be the Glory” (life lived for God’s glory alone).
Read the whole post.