They are learning a life lesson about god and them selfs
A flat character is a character that does not change throughout the book or movie so even though I have not read that book or watched the movie, I would guess it is because he does the change throughout the book. Hope this helps! シ
Courageous and determined
The lines are explaining how even though our hearts are beating, they are beating us all the way to the grave. The heart beat is compared to the rhythm of a funeral march with everyone stepping in time. The lines are showing hearts are beating courageously and with determination all the way to the person's death, which is inevitable.