"Genius"  was, of course a word dear to the Romantic movement. Barfield uses it sparingly but with emphasis.

In What Coleridge Thought, for example, he quotes Coleridge on genius approvingly.

In Man the centripetal and individualizing tendency of all Nature is itself concentrated and individualized--he is a revelation of Nature! Henceforward he is referred to himself, delivered up to his own charge; and he who stands the most on himself, and stands the firmest, is the truest, because the most individual, Man. In social and political life this acme is interdependence; in moral life it is independence; in intellectual life it is genius. (Coleridge, quoted in WCT 68)
In Speaker's Meaning, Barfield supplies his own history of the concept, attempting to ascertain its significance for the evolution of consciousness.
We must say . . . that the history of poetic psychology is the story of a superindividual psychology, which extends from as far back as can be investigated up to at least the Renaissance, but with reverberations still going on much later; and which only then begins to be transformed into something like an individual psychology. Then it becomes, or begins to become, a psychology of individual "genius." And so the word "genius" changes its meaning. Originally the genius was a spirit-being, other than the poet himself (though certainly with a special relation to the poet himself); but that is not what we mean by genius today. The Romans (for it is a Latin word) would never have said of a man he is a genius. They would have said that he had, or was accompanied or inspired by, a genius. We prefer to say that he is one. (SM 78)
See in particular Speaker's Meaning, Chap. 3.