well the whole idea bout this album is that it centers on the story of a cancer patient who is close to dying... (the lead singer has a fascination with deadth) in the song welcome to the black parade the patient after learning of his illness, reflecting on his life, and dealing with all the issues of mortality, the Patient's own mortality is quickly coming to an end. Here the Patient is drifting between life and death, and so death is coming for him in the form of his strongest memory. The Patient's fondest memory is of his father taking him to town as a boy to see a parade ("when I was a young boy, my father took me into the city, to see a marching band"). The Patient's father asks him as a boy "Son, when you grow up, would you be the savior of the broken, the beaten, and the damned?", perhaps preparing the Patient for his future illness, and asking him if he will have what it takes to mentally overcome it and be an example for others who follow in his footsteps to be strong. The Patient's father also tells him "someday I'll leave you a phantom, to lead you in the summer, to join the Black Parade." This hints that the Patient's father most likely died before the Patient, and will help him join the Black Parade (in other words be there when he dies to help him in the afterlife). The song also shows that the Patient most likely had a very good relationship with his father, since his fondest memory in life occured when he was with his father. This is the opposite of the relationship he has with his mother, which is further detailed in the song Mama.
The Patient passes into a realm of life and death, and sees the Black Parade. The Black Parade seems to take place in the city that he saw the marching band in his youth, only now the city is barren, and more macabre ("the bodies in the street"). He sees the performers of the Black Parade, only they too are more macabre than those of the parade he saw in his youth, and seem to represent emotions and other parts of his life. The Black Parade tell him of "the disappointed faces of your peers", which have no effect on the Patient, as he states he "could not care at all", showing he will no longer let anyone dictate his actions, and hasn't quite repented yet (as he does in Famous Last Words). He still doubts himself ("I'm just a man, I'm not a hero" in reference to his father's question at the beginning of the song). He is still firm in his doubt of the world ("you can try, you'll never break me"). Finally The Black Parade insures him that his "memory will carry on", and though he may be dead and defeated his "weary widow marches on." Thus trying to encourage him that he isn't as evil as he thinks, and that if he joins them what he leaves behind in life will be fine.