A--- The Prophet (Peace be upon him) explained it when asked about it by Gabriel (Peace be upon him) saying: "That you worship Allah as if you are seeing Him, for though you don't see Him, He, verily, sees you." (Bukhari and Muslim) Thus, the Prophet (Peace be upon him) explained that there are two different ranks:

First: The Seeing rank: that the worshiper acts upon his seeing of Allah the Almighty with his heart. This means that the heart gets illuminated with the light of faith, the insight gets sharper till the unseen becomes visible before his eyes. Verily, this is the reality of the Ihsan (Perfection of Faith) rank.

Second: The Watching rank: that the worshipper recalls the Watching of Allah over him and His Nearness and Knowing of all things (pertaining to him). Upon this, if the worshipper recalls this while acting and acted thereupon, he will be loyal to Allah. This is because this prevents him from caring for other than Allah the Almighty upon performing acts. The reward of the people of these two ranks differs according to each one's pure and live insight.