This idea is so, so important to the series in general, and Brook in particular. There are times in One Piece where people die for noble causes, and others where people act knowing that there's a good chance that they could die, but knowingly choosing death over life is never portrayed in a positive light.
As someone who views One Piece through the lens of Romantic literature, this is really important because historically the Romantics, er, well, romanticized suicide and death and the historic last stand. It's doubly interesting to me as a Japanese story, with Japan having its own long, complicated history with the concept of honorable death.
One Piece directly challenges both of these ideas, with life and living being romanticized instead, even if that means you have to get on your knees and beg for it like Brook does with Ryuma later on.
And it's a tightrope that story has to balance. Nami willingly lived under to boot of the man who killed her mother for years, but there came a time when enough was enough, and both she and the village had to stand up and fight for her freedom. She carried that lesson to her fight with Enel, even though she was hopelessly outmatched and would have been reduced to a greasy smear if Luffy hadn't shown up to save her. Within the context of the story both instances were portrayed positively, with Oda indicating through his writing that she had made the correct decision.
But that's not what's happening here. This is Luffy being willing to run away at Sabaody because he knew the Pacificas were too strong. This is Usopp lambasting the samurai at Wano for rushing toward their deaths rather than living to fight another day.
It's Brook knowing he made a promise to a friend, and doing everything in his power to keep it, even if it meant looking like a sniveling coward groveling at the feet of his own shadow.
