He first asked, "Tell me, what is Submission (which is the meaning of the arabic word, Islam)?" The Prophet answered it by listing what became popularly known as the five pillars of Islam: testimony of faith, daily prayer, charity, fasting, and pilgrimage. To the surprise of those watching, this unknown questioner said, "You are correct."
Next he asked what faith is (iman), to which the Prophet answered by listing the five items of belief: in God, in the angels, in the Scriptures, in the Prophets, and in the Last Day and Hereafter. Again the questioner responded, "You are right."
Then he asked, "What is [mastery of] virtue (ihsan)?" To which the Prophet answered, "[Mastery of] virtue is to worship God as if you see Him; and if you don't see Him, then [worship Him with the conviction that] He sees you."
This saying is an outlining of a path of religious or spiritual EVOLUTION, FROM A MERE EXTERNAL OBSERVATION OF RELIGIOSITY TO AN INNER EXPRESSION OF FAITH TO A STATE OF INTIMACY WITH GOD.
Even among the religious, not all human souls are inclined to intimacy with God, any more than all souls are drawn to be expert in medicine. And among those who desire divine intimacy, few are capable of the self-discipline and hard work that is demanded of them to achieve it, just as few who want to become doctors are truly capable of expending the effort.
Excerpt from "What's Right with Islam: A New Vision for Muslims and the West", by Imam Feisal Abdul Rauf. Published by Harper San Francisco).
