Why is there so much time spent describing the black box? What are 2 details about the black box

Shirley Jackson spends so much time describing the black box because it is a symbol of the lottery itself: something the village clings to despite the fact that the original was lost.
The box that the villagers use to store the lots that people draw isn't the original box; that was lost long ago. Despite the fact that the original was lost and it is only rumored that a piece of the original was used to construct the new one, the town will not allow it to be replaced with a new one. The narrator says:

The original paraphernalia for the lottery had been lost long ago, and the black box now resting on the stool had been put into use even before Old Man Warner, the oldest man in town, was born. Mr. Summers spoke frequently to the villagers about making a new box, but no one liked to upset even as much tradition as was represented by the black box. There was a story that the present box had been made with some pieces of the box that had preceded it, the one that had been constructed when the first people settled down to make a village here. Every year, after the lottery, Mr. Summers began talking again about a new box, but every year the subject was allowed to fade off without anything's being done.

The lottery itself is like the box. There is no talk of doing away with it; instead, the townspeople gather to perform the grim ritual as if it is completely normal. The people long ago lost the understanding of why the lottery happens. Despite that, the people cling to the lottery and perform it even though there would seemingly be no consequences if the town decided not to.
Jackson says the box is made of black wood. She also says that the box is so old that it is splintered on one side; the original color of the wood is showing through. In other places, it is faded or stained.