Highmindedness, a jealousy for good
Noisome alley
"Noisome" means foul-smelling, not just noisy. Keats places nobility in stinking slums and wilderness—places polite society ignores.
Hooded shame
The hood references monks or executioners. The money-grubbers should hide their faces like criminals or hypocrites.
Native sty
A sty is a pig pen. Envy and Malice aren't just defeated—they're driven back to their natural habitat: filth.
Still applause
"Still" means silent here. The unnumbered souls applaud without sound—a spiritual rather than public recognition.