John Cassian, The Institutes XII.5: That incentives to all sins spring from pride

This is the reason of the first fall, and the starting point of the original malady, which again insinuating itself into the first man, through him who had already been destroyed by it, produced the weaknesses and materials of all faults. For while he believed that by the freedom of his will and by his own efforts he could obtain the glory of Deity, he actually lost that glory which he already possessed through the free gift of the Creator.