“every good piece of art, to whichever of these ends it may be directed, involves first essentially the evidence of human skill and the formation of an actually beautiful thing by it.”
Ruskin makes skilled human making and achieved beauty basic components of good art, foregrounding workmanship before his additional demands for truth or usefulness.
Source details
Lectures on Art, Lecture IV, Project Gutenberg #19164. The sentence belongs to Ruskin’s own theory of artistic quality.