People
Grace is the absence of every thing that indicates pain or difficulty, or hesitation or incongruity.
— William Hazlitt · "On Beauty" The Round Table (1815-1817)

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
Grace, here, is defined by what's missing: no sign of strain, difficulty, hesitation or awkwardness. When a movement or manner looks graceful, it's because effort and mismatch have vanished from view. It's beauty described as smoothness, the absence of anything jarring.
Context reviewed