Did you read the introduction? It says: Weil wrote this fourteen-page letter to Simone Weil, his sister ... (Keep in mind that the letter was not written for a mathematician, even though Simone could not understand most of it.)
And without that context, his sister may have been perplexed as to why he would dive into complicated math that he should have known she wouldn't understand. Consider that sometimes when you read ego or aggression into writing, it's not coming from the author's mind but is a projection of your own.
