Man is so shrouded in the darkness of errors that he hardly begins to grasp through this natural law what worship is acceptable to God.

Surely he is very far removed from a true estimate of it. Besides this, he is so puffed up with haughtiness and ambition, and so blinded by self-love, that he is as yet unable to look upon himself and, as it were, to descend within himself, that he may humble and abase himself and confess his own miserable condition.

Accordingly (because it is necessary both for our dullness and for our arrogance), the Lord has provided us with a written law to give us a clearer witness of what was too obscure in the natural law, shake off our listlessness, and strike more vigorously our mind and memory.

—John Calvin
Institutes, 2.8.1