I don't think it's very much worth thinking about. It's a pseudointellectual quip that sounds superficially insightful but which holds zero substance.

The overwhelming majority of humanity's problems, such as they might be described, stem from the biological drive to survive and procreate. The quip presupposes that man naturally has a room to sit quietly in; this is not the case. The procurement of a room to sit in requires a significant amount of effort. It can entail the securing of territory and building of the shelter oneself, or it can entail the education, advanced skill development, and daily labour required to pay to reap the results of other people having secured the territory and built the shelter. To say nothing of food, mating, and rearing of offspring.

Pascal was born well-to-do, so perhaps he was removed from the general human experience. He was provided with the room to sit quietly in by the efforts of others, and may never have had to work a day in his life, affording him the luxury to make that statement. He also did not marry or reproduce. If everyone had lived the life he lived, there would be no rooms to sit in and indeed no men to sit in them. Being charitable, I suppose it's true that if all mankind were to stop reproducing, there would shortly be no more problems for humanity on account of humanity no longer existing.