It seems as if the Radley house is watching the rest of the world go by. How might this observation become critical to Jem and Scout in the future?
As Scout and Jem mature in the novel, they move away from their childish impressions of Boo Radley, the Radley family in general, and their fear of the Radley house. Scout's description from Chapter One states:
The Radley Place jutted into a sharp curve beyond our house. Walking south, one faced its porch; the sidewalk turned and ran beside the lot. The house was low, was once white with a deep front porch and green shutters, but had long ago darkened to the color of the slate-gray yard around it. Rain-rotted shingles drooped over the eaves of the veranda; oak trees kept the sun away. The remains of a picket drunkenly guarded the front yard "swept" yard that was never swept-where johnson grass and rabbit-tobacco grew in abundance.
Inside the house lived a malevolent phantom. People said he existed, but Jem and I had never seen him.
As they grow, they come to understand that Boo Radley has watched them throughout their lives. He covers Scout with a blanket on the night of the fire, but she doesn't even see him. He leaves several gifts for them in the knothole of the tree, and they only gradually realize it's him. When the hole is cemented, Jem is gripped with a rage he's never felt before. They are Boo's connection to the rest of the world- the only connection he wants. As Scout articulates at the end of the story, forcing Boo out into the world would be like shooting a mockingbird. He prefers to remain indoors, isolated, living vicariously through Scout and Jem.