There are things one cannot express, perhaps, but that can be grasped emotionally or intuitively.
But the union of the knower and the known is beyond even such a nonintellectual, intuitive understanding.
There are many things that may be considered a single entity from one point of view and a multiplicity from another point of view.
This refers to anything, in fact, that can be taken apart into single units and includes most of the objects around us.
In contrast, the unity of knowledge and the knower is not given to separation.
When a person learns something, he embraces it and is embraced by it.
This was explained by one of the disciples of Baal HaTanya by the image of two drops of water on the window sill.
When they meet and merge, it is hard to say which drop absorbed the other.
They become an indissoluble single larger drop of water that cannot be separated again into its previous components.
Thus it is with the known and the knower, that which is contained and that which contains, the finite and the infinite.
–Rabbi Adin Steinsaltz
From The Sustaining Utterance by Rabbi Adin Steinsaltz