Their roles are clearly distinct. Whatever action happens — the entire chain of cause and effect — Prakriti is responsible for it. Prakriti does the doing.
But the experience of pleasure and pain belongs to Purusha, the soul. Think of a theater. The stage, the lights, the costumes, the set design — all of that is Prakriti's work. But the one in the audience who laughs or weeps — the one who actually experiences — that is Purusha.