Description uses the five senses of sight, sound, taste, touch, and smell to place a reader in a scene. Hughes starts by offering a very generalized description of a revival meeting. It could be any revival, with

preaching, singing, praying, and shouting, and some very hardened sinners had been brought to Christ, and the membership of the church had grown by leaps and bounds.

It's as if Hughes wants to deliberately distance us from any specifics. However, when it comes to the children being brought up to be saved, the concrete descriptive details appear, pointing to this part of the essay as describing a specific salvation experience. Examples of such descriptive details include the preacher holding

out his arms to all us young sinners there on the mourners' bench

As the camera, so to speak, zooms in on Langston's individual experience, he lets us see, too,

old women with jet-black faces and braided hair, old men with work-gnarled hands

We also hear the specific words of a hymn being sung.

Hughes frames his own trauma, in which he lies about being converted so as not to cause too much of a problem and to live up to expectations, within a generic experience of revival meeting. Although Hughes's anguish is his own, the way the description is handled suggests this happens in many places to many people.