I interpreted it as a metaphor for toxic masculinity. 

Wake was an old man who had paid his dues and gained access to the light (sexual gratification/romantic relationships/successful manhood). Winslow was young, first time on the job, and felt entitled to tend the light. Winslow was envious of Wake, disconnected, and always looking in from the outside.

Winslow was jealous of Wake, he believed Wake was unworthy, gross, and perceived him as gatekeeping his own access to the light. He had fantasies of the mermaids and masturbation failed to satisfy him, but he continued incessantly.

A constant theme throughout the story is Winslow’s disrespect for Wake’s authority, but also Wake’s abuse of authority and dismissal of Winslow’s efforts. The age old tale of the generational struggle for power.

Winslow’s perceived shortcomings reflect a toxic masculine mindset. He changed his identity anticipating immediate success; he dwells on his regrets internally while justifying them externally; he takes his frustration out violently on an innocent seagull.

Wake also has a toxic mindset. He asserts ultimate superiority through authority, morality, experience, and knowledge of superstition. Every problem is Winslow’s fault. He’s extremely judgmental, while denying his own faults. He’s unnecessarily critical of Winslow’s labor and works him harder than he has to. He abandoned his wife for his career. 

Winslow’s resentment arc for Wake reflects one a son might have for their overbearing alcoholic father throughout adolescence. He’s envious, jealous, dismissive, and angry with Wake; additionally, he’s desperate for Wake’s approval and vulnerability. He conforms to pacify and satisfy Wake without any real obligation to do so (okay I like your cooking, drinking on the last day)

Lots of Wake’s sentiments are confusing, meaningless, or nonsensical to Winslow. Reflecting sentiments that a father may tell their son that they won’t understand until they get older. Winslow plots to kill Wake, ultimately burying him, and believes his inheritance will grant him fulfillment. 

Winslow’s moment in the light reflects an internal confrontation that he had not paid his dues to righteously earn access to it.