Before Feuerbach, There Was al-Shaykh al-Akbar (d. 1240 CE)

Since there are as many cups as drinkers at the Pool which will be found in the abode of the hereafter, and since the water in the cup takes the form of the cup in both shape and color, we know for certain that knowledge of God takes on the measure of your view, your preparedness, and what you are in yourself. No two people will ever come together in a single knowledge of God in all respects, since a single constitution is never found in two different people, nor can there be such a thing. When there are two, there must be that through which the distinction is made, since the entity of each is immutably established. Were this not so, they could not be two. Hence no one ever knows anything of the Real except his own self.

[Quoted in Chittick, The Sufi Path of Knowledge (1989), 342].