Justification: The Hinge

Calvin, in the Institutes, sets out to do justice to the doctrine of Justification. Though he had covered it before, he feels it necessary to broaden his teaching. Why? 3.11.1:

(Justification) is the main hinge on which religion turns, so that we devote the greater attention and care to it. For unless you first of all grasp what your relationship to God is, and the nature of his judgment concerning you, you have neither a foundation on which to establish your salvation nor one on which to build piety toward God.