In Chapter 9 of Harper Lee's To Kill a Mockingbird, Uncle Jack is creating a biblical allusion when he says to Atticus, "Let this cup pass from you, eh?"
We read in the gospels of Matthew, Mark, and Luke that just after Jesus's last Seder, a feast that marks the start of Passover, just prior to his crucifixion, Jesus leads a few of his disciples to the Garden of Gethsemane to pray. While praying, Jesus asks God the Father, "My father, if it is possible, let this cup pass from Me; yet not as I will, but as You will" (Matt 26:39; Mrk 14:36; Lk 22:42). Shortly after praying, Jesus is betrayed by Judas and arrested by the Romans. During a Seder, drinking from a cup of wine has symbolic meaning. Four toasts are made to God from four cups of wine in celebration of God's four expressions of redemption. Hence, when Jesus asks God, "Let this cup pass from me," he is metaphorically asking to be permitted not to drink a toast from the particular cup he is metaphorically being handed in celebration of redemption because he does not want to do the deed that will lead to that redemption. In other words, Jesus knows God's people will be redeemed through his upcoming death, and he is asking to be permitted to escape that death. The phrase "let this cup pass" has become a euphemism to mean "let me escape this horrible event," but for Jesus, the "cup," or horrible event, is specifically tied to the salvation of God's people.
In To Kill a Mockingbird, Uncle Jack uses the words "let this cup pass" to mean something similar to Jesus's own words. Atticus had just explained that Tom Robinson's case is hopeless because the evidence consists of nothing but Robinson's words against the Ewells'. Yet, Atticus hopes to at least "jar the jury a bit" and appeal to the higher courts. He further confides that he had "hoped to get through life without a case of this kind," meaning that he had hoped to escape having to suffer through trying to defend an innocent African-American man before a racially prejudiced jury. He knows that in doing so, he is offering himself up as a great sacrifice to society because, even though he is acting to try and preserve the life of an innocent man, society's prejudiced members will metaphorically tear Atticus and his children to bits through their ridicule. Uncle Jack follows Atticus's comment that he had hoped to avoid a case like this with his question, "Let this cup pass from you, eh?" In so doing, Uncle Jack is implying he understands Atticus is making a painful sacrifice that, like Jesus, he would prefer to avoid. Yet, Atticus knows he must go through with his defense of Robinson because, like Jesus, Atticus understands sacrificing himself is the only morally correct thing to do.