From Buber’s Between Man and Man:

Sometimes I hear it said that every I and Thou is only superficial, deep down word and response cease to exist, there is only the one primal being unconfronted by another. We should plunge into the silent unity, but for the rest leave its relativity to the life to be lived, instead of imposing on it this absolutized I and absolutized Thou with their dialogue.

Now from my own unforgettable experience I know well that there is a state in which the bonds of the personal nature of life seem to have fallen away from us and we experience an undivided unity. But I do not know — what the soul willingly imagines and indeed is bound to imagine (mine too once did it) — that in this I had attained to a union with the primal being or the godhead. That is an exaggeration no longer permitted to the responsible understanding. Responsibly — that is, as a man holding his ground before reality — I can elicit from those experiences only that in them I reached an undifferentiable unity of myself without form or content. I may call this an original pre-biographical unity and suppose that it is hidden unchanged beneath all biographical change, all development and complication of the soul. Nevertheless, in the honest and sober account of the responsible understanding this unity is nothing but the unity of this soul of mine, whose “ground” I have reached, so much so, beneath all formations and contents, that my spirit has no choice but to understand it as the groundless. But the basic unity of my own soul is certainly beyond the reach of all the multiplicity it has hitherto received from life, though not in the least beyond individuation, or the multiplicity of all the souls in the world of which it is one — existing but once, single, unique, irreducible, this creaturely one: one of the human souls and not the “soul of the All”; a defined and particular being and not “Being”; the creaturely basic unity of a creature, bound to God as in the instant before release the creature is to the creator spiritus, not bound to God as the creature to the creator spiritus in the moment of release.

The unity of his own self is not distinguishable in the man’s feeling from unity in general. For he who in the act or event of absorption is sunk beneath the realm of all multiplicity that holds sway in the soul cannot experience the cessation of multiplicity except as unity itself. That is, he experiences the cessation of his own multiplicity as the cessation of mutuality, as revealed or fulfilled absence of otherness. The being which has become one can no longer understand itself on this side of individuation nor indeed on this side of I and Thou. For to the border experience of the soul “one” must apparently mean the same as “the One”.

But in the actuality of lived life the man in such a moment is not above but beneath the creaturely situation, which is mightier and truer than all ecstasies. He is not above but beneath dialogue. He is not nearer the God who is hidden above I and Thou, and he is farther from the God who is turned to men and who gives himself as the I to a Thou and the Thou to an I, than that other who in prayer and service and life does not step out of the position of confrontation and awaits no wordless unity, except that which perhaps bodily death discloses.

Nevertheless, even he who lives the life of dialogue knows a lived unity: the unity of life, as that which once truly won is no more torn by any changes, not ripped asunder into the everyday creaturely life and the “deified” exalted hours; the unity of unbroken, raptureless perseverance in concreteness, in which the word is heard and a stammering answer dared.