The Duties of the Heart, by Rabbi Bachye, tr. by Edwin Collins, [1909], at sacred-texts.com
The Motive Forces that Impel Man to Grateful Service
There are two distinct motive forces impelling man to humble and grateful service of God. One of them is inherent in human reason, implanted in man's intelligence, and hidden deep within the very roots of his being; the second is acquired by means of his hearing and understanding. This second is the Torah. *
The service due to the humility of hope and fear is that which arises from the acquired, external motive which enforces the obligation with rewards and punishments in this world and in the world to come; the second kind is induced by the working of the hidden motive force of Reason, innate in human nature, and bound up with the union of man's soul to his body. Both kinds of humility are praiseworthy, and both lead to a right way of life and conduct; but the one is the complement of the other, and the motive of the Torah is the stepping-stone to both, while the motive of Reason, and the way of proof, is the preferable and nearer to God.
The service undertaken at the prompting of
[paragraph continues] Reason is free from all suspicion of hypocrisy, and from all admixture of hope or fear. It springs from a philosophic knowledge of how the creature is indebted to the Creator, and is not restricted to actual outward acts, but will include the ethical working of the heart and mind—the fulfilment of the duties of the heart.