Think about this for a minute. “It is only necessary to negate something that is possible, not something that is impossible. Thus, when G‑d said “My face may not be seen,” He meant that the workings of Divine providence can be perceived, but not directly.
To explain: There are two ways of grasping a concept: by understanding what it is and by understanding what it is not. If a concept is within our sphere of experience, we can understand what it is. If a concept is outside our sphere of experience, we cannot understand what it is, but we can understand what it is not. We mentally remove it from possibility after possibility until, by process of elimination, we gain a glimpse of it.
Thus, G‑d’s statement, “My face may not be seen,” means that we cannot understand Divine providence directly, but we can understand it by negating what we know it not to be.1Sefer HaSichot 5748, vol. 1, pp. 299–300.
Moses asked G‑d further to show Him how everything He does is out of kindness. G‑d replied that it is only possible for the human mind to grasp this “from the back,” i.e., after the fact
[G‑d told Moses,] “You may see My ‘back,’ but My ‘face’ may not be seen.” Exodus 33:23