Great quote posted on Monergism.com :

” … it is wrong to suppose that the doctrine of Justification by faith alone, that storm center of the Reformation, was the crucial question in the minds of such theologians as Martin Luther, Ulrich Zwingli, Martin Bucer, and John Calvin. This doctrine was important to the Reformers because it helped to express and to safeguard their answer to another, more vital, question, namely, whether sinners are wholly helpless in their sin, and whether God is to be thought of as saving them by free, unconditional, invincible grace, not only justifying them for Christs’ sake when they come to faith, but also raising them from the death of sin by His quickening Spirit in order to bring them to faith.” – Michael Haykin