I can help you try to explain and identify all four phrases in Langston Hughes’ short story “Salvation.”
Phrase 1: “the ninety and nine safe in the fold”
This part is related to the preacher. The narrator is listening to the preacher sing a song about how 99 lambs are safe but one lamb is left out in the cold. This lamb doesn’t not have shelter or protection. This lamb has to fend for itself. You could argue this lamb symbolizes the narrator. The narrator seems to be the only one unsure about this salvation business.
Phrase 2: “the lower lights are burning”
This phrase also involves a song. This song, too, seems to deal with salvation and damnation. The burning makes me think of hell. The lower lights make me think of hell as well since hell is usually depicted as something that’s below, beneath, or lower.
Phrase 3: “a rounder’s son”
Westley is a rounder’s son. A rounder is someone who drinks and spends a lot of their time at bars. The narrator is not in good company. The narrator’s connection to Westley might say something about the narrator’s own questionable character.
Phrase 4: “knickerbockered legs”
The “knickerbockered legs” describes the legs of Westley. Remember, Westley gets tired of sitting. Out of boredom and restlessness, Westley gets up to be saved. The narrator observes Westley “swinging his knickerbockered legs” and grinning at him. Such a portrayal gives Westley a rather trollish, ghoulish, and maybe even demonic nature. It’s like Westley is taunting the narrator.
If you wanted to focus on the “knickerbockered” part, you could do some research into the history of knickerbockers. They were pants worn by Dutch settlers in the New World. One of the goals of many settlers was to convert the Indigenous people to Christianity. You could argue Westley assimilates into the settlers'/colonizers' belief system by being saved. Although, you should probably say something about the real reasons for Westley’s salvation.