denial or rejection: a denial or rejection of something, usually for moral or religious reasons
declaration giving something up: an official declaration giving up a title, office, claim, or privilege
More into context:
(…) Pascal underwent some kind of mystical experience. He sewed a description of the event into his coat so that he could wear it next to his heart, claiming “Renunciation, total and sweet.” He abandoned mathematics and physics, swore off high living, dropped his old friends, sold all his possessions except for his religious books, and, a short while later, took up residence in the monastery of Port-Royal in Paris.
(…) Pascal wrote back in August:
I can scarcely remember that there is such a thing as Geometry (i.e. mathematics). I recognize Geometry to be so useless that I can find little difference between a man who is a geometrician and a clever craftsman. Although I call it the best craft in the world it is, after all, nothing else but a craft…It is quite possible I shall never think of it again.
Did he just go bonkers along the way? Was that a warning to those who think too much?