The answer is: the book will bear witness to events that must be known.
"Night" is an autobiographical novel by Elie Wiesel, who accounts his struggle as a prisoner during the Holocaust. He desires to make sure the world acknowledges what happened in concentration camps as he narrates how crude society was and how inhuman even prisoners became towards one another - mostly attemping to survive themselves.
In my opinion, the whole poem is quite ironic - although she is mentioning the exultation and the royal color of death, the poem itself begins with the narrator saying that she cannot breathe - that she doesn't want to die.
So, I would say that the ironic parts are:
Exultation is the going
Of an inland soul to sea, -
Past the houses, past the headlands,
Into deep eternity!
