If you're asking for main idea, the main idea or thesis statement sentence is sentence 1, where they explain what the passage is about.
It's been a while since I've read the book and I don't really a lot of the context, so just from this passage I would say it says he notices nice houses and other people's wealth and maybe envies them a little bit. (although you don't get that explicitly from this passage.)
Answer:
Alex had helped poor people
Alex is helping poor people
The Power or Sympathy is a sentimental novel, dealing with domestic life.
I hope it helps!
