"How much of a person a man is depends on how strong the I of the basic word I-You is in the human duality of his I.

The way he says I - what he means when he says I - decides where a man belongs and where he goes. The word "I" is the true shibboleth of humanity.

Listen to it!

How dissonant the I of the ego sounds! When it issues from tragic lips, tense with some self-contradiction that they try to hold back, it can move us to great pity. When it issues from chaotic lips that savagely, heedlessly, unconsciously represent contradiction, it can make us shudder. When the lips are vain and smooth, it sounds embarrassing or disgusting.

Those who pronounce the severed I, wallowing in the capital letter, uncover the shame of the world spirit that has been debased to mere spirituality.

But how beautiful and legitimate the vivid and emphatic I of Socrates sounds! It is the I of infinite conversation, and the air of conversation is present on all its ways, even before his judges, even in the final hour in prison. This I lived in that relation to man which is embodied in conversation. It believed in the actuality of men and went out toward them. Thus it stood together with them in actuality and is never severed from it. Even solitude cannot spell forsakenness, and when the human world falls silent for him, he hears his daimonion say You.

How beautiful and legitimate the full I of Goethe sounds! It is the I of pure intercourse with nature. Nature yields to it and speaks ceaselessly with it; she reveals here mysteries to it and yet does not betray her mystery. It believes in her and says to the rose: "So it is You" - and at once shares the same actuality with the rose. Hence, when it returns to itself, the spirit of actuality stays with it; the vision of the sun clings to the blessed eye that recalls its own likeness to the sun, and the friendship of the elements accompanies man into the calm of dying and rebirth.

Thus the "adequate, true, and pure" I-saying of the representatives of association, the Socratic and the Goethean persons, resounds through the ages.

And to anticipate and choose an image from the realm of unconditional relation: how powerful, even overpowering, is Jesus' I-saying, and how legitimate to the point of being a matter of course! For it is the I of the unconditional relation in which man calls his You "Father" in such a way that he himself becomes nothing but a son. Whenever he says I, he can only mean the I of the holy basic word that has become unconditional for him. If detachment ever touches him, it is surpassed by association, and it is from this that he speaks to others. In vain you seek to reduce this I to something that derives its power from itself, nor can you limit this You to anything that dwells in us. Both once again deactualize the actual, the present relation, I and You remain; everyone can speak the You and then becomes I; everyone can say Father and then becomes son; actuality abides.

(Buber, p. 117, 1970)

I think the reference is - Buber, M. (1970). I and Thou.  New York: Charles Scribners's Sons.

Love Jack.