"there was a mildness about his mouth and eyes that proclaimed no devil" --> inherent goodness and purity to his character
Also aligns with the his initial portrayal of Ralph as a character untouched by darker instincts: symbolises his pure intentions and genuine desire to maintain order and civilisation on the island
emphasises the absence of evil and malevolent intentions; contrasts him against other characters
however could also serve as a form of foreshadowing, and opens a theme of evil
acts as a manifestation of his moral compass, and desire to maintain principles of order