In the original, punto vivo, literally living point: the place in Vitangelo that goes on feeling when the images he makes of himself are removed. Dida's laughter wounds it in Book V, and Vitangelo himself names it, in Book VII, as God, who in him does not tolerate being taken for a usurer. The novel does not say whether it is a soul or a will.
Where It Appears
Quotes
Apart from every image in which I could picture myself alive to myself, as someone for myself too, apart from every image of myself as I imagined I might be to others, a “vital point” in me had felt itself wounded so deeply that I lost the light of my eyes.
Well, but this, precisely this, was the “vital point” wounded in me, which blinded me and at that moment took from me the understanding of everything: that I was not a usurer, that usurer I had never been for myself, and now I no longer wanted to be one even for others, and would no longer be one, even at the cost of the ruin of every condition of my life.
Book V: The vital point, Vitangelo Moscarda, on the reason he cannot tell Quantorzo
That vital point that had felt itself wounded in me, when my wife laughed on hearing me say that I no longer wanted to be counted as a usurer in Richieri, was God, beyond any doubt: God, who had felt himself wounded in me, God, who in me could no longer bear that others, in Richieri, should count me as a usurer.