John Calvin, Institutes of the Christian Religion:
…the pious mind realizes that the punishment of the impious and wicked and the reward of life eternal for the righteous equally pertain to God’s glory. Besides, this mind restrains itself from sinning, not out of dread of punishment alone; but, because it loves and reveres God as Father, it worships and adores him as Lord. Even if there were no hell, it would still shudder at offending him alone.
Here indeed is pure and real religion: faith so joined with an earnest fear of God that this fear also embraces willing reverence, and carries with it such legitimate worship as is prescribed in the law. And we ought to note this fact even more diligently: all men have a vague general revelation for God, but very few really reverence him; and wherever there is great ostentation in ceremonies, sincerity of heart is rare indeed.
Words of Grace 