The Reformation called the church back to faith in Christ as the sole mediator between God and man. While the Roman Catholic Church held that “there is a purgatory and that the souls there detained are helped by the intercessions of the faithful,” and that “saints are to be venerated and invoked” and “their relics are to be venerated,” the Reformers taught that salvation was by Christ’s work alone. As John Calvin said in the Institutes of the Christian Religion, “Christ stepped in, took the punishment upon himself and bore the judgment due to sinners. With his own blood he expiated the sins which made them enemies of God and thereby satisfied him. . . . We look to Christ alone for divine favour and fatherly love!”
Likewise the Heidelberg Catechism, asks, “Do such then believe in Jesus the only Saviour who seek their salvation and happiness in saints, in themselves, or anywhere else?” It answers, “They do not; for though they boast of him in words yet in deeds they deny Jesus the only deliverer and Saviour: for one of these two things must be true that either Jesus is not a complete Saviour or that they who by a true faith receive this Saviour must find all things in him necessary to their salvation.”
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.