Your question is definitely confusing because Darryl Pinckney is best known for the following works: High Cotton, Sold and Gone, Out there, The Forest, Orlando, and Time Rocker. However, because he was also an essayist and freelance writer, I assume you mean the article "The Last New Negro" published in the March 1989 issue of The New York Review. I will focus my answer on that particular work.
The very first sentence of "The Last New Negro" goes far in explaining the main idea:
Sterling A. Brown was one of the few black writers of his generation who did not want to be part of the Harlem Renaissance.
Put simply, the article is about Sterling Brown who prided himself in being both black and separate from the Harlem Renaissance (instead of being proud of it). In fact, Brown always called the Harlem Renaissance a "publishers' gimmick." Why? It wasn't long enough to warrant the title "renaissance," and it didn't contain hardly anyone native of Harlem! Brown attests that those part of the Harlem Renaissance basically gained prominence by hobnobbing with whites while Brown, himself, decided to get to the real meat of the matter:
Sterling himself was down in Lynchburg, Virginia, talking to a guitar player, Big Boy Davis, one of the rural characters whose ethos engaged Sterling’s melancholy and rebellious sensibility, from which came a folk poetry of lasting originality.
It is then in the article when Pinckney goes into Brown's entire life story. Brown was born in 1901, and his dad had been a slave. Surpassing all odds, Brown became both a preacher and a professor. He his known for constantly teaching, no matter what job occupied his time at the moment.
Pinckney attests that Brown remains almost completely unknown while he should be vastly honored. Brown was not only always teaching, but he was a genius in relating folklore.
They used to say that every black in the United States knew every other black, and Sterling was one of those who had stories about everyone, from Jelly Roll Morton to a raconteur barber in Nashville.
Further, Pickney believes that Brown was a true black historian, and one of the few that can be called such. Pickney's article gives honor where honor is due to Brown: someone worthy to be called "the Last New Negro."