Very often, Ali would sob the whole night in prayers to God, and God would reward him with a glimpse of the Inner Vision. According to Ali, the highest purpose of knowledge is the awakening of latent spiritual faculties whereby one is enabled to discover his true and inner self. It is to this inner self that God reveals Himself when the self disappears in the vision of the "All Absorbing Reality." Ali often observed that man could have the joy and wonder of communion with God if one abandoned pride, disciplined the flesh, overcame the lust and submitted to the Will of God. He exhorted the people in his various sermons not to indulge in the gross licentiousness, which had characterized Arab society in the "Days of Ignorance." But should instead live in piety and simplicity as enjoined by Islam. Ali said, "Man is a wave in the boundless Sea of God. As long as man's vision is clouded by ignorance and sensuality he will consider himself a separate entity, different from God. But when the veil between him and God is lifted, he will then know what he really is, the wave will then merge with the ocean". Ali held that enlightenment is needed so that one can first get to know himself. Only then would he get to know God. Ali held that to this end religious exercises must be practiced. Sufism for which Ali stood derived its strength from the Shariah. Ali preached that any form of knowledge which failed to show the Infinite Reality in man was useless, because it could not fill that vacuum of which the aching soul of every individual was so pathetically conscious. Ali wanted men to be virtuous as virtues purify the soul, and it is only the purified soul that can be the recipient of spiritual enlightenment. This is the doctrine of Inner Light, which was enunciated by Ali as the core of Sufi thought. Ali is accordingly acknowledged as the "Father of Sufism" and the "Prince of Saints".