The Fire Next Time has already been mentioned. You can read part of it as published in the New Yorker: https://www.newyorker.com/magazine/1962/11/17/letter-from-a-...

In addittion to The Fire Next Time, my personal favorites are a series of essays he wrote from the South during desegregation:

A Fly in the Buttermilk

Nobody Knows My Name

Faulkner and Desegregation

The Fire Next Time, IMO is a good entrypoint.

Go tell it on the mountain, it was his first book and lays the foundation for everything he did later. Amazing book