"we did not feel prepared to be the heirs of such a terrifying hour, but within it, we found the power to autho a new chapter." what does this refer to?

even though there may be variations in human emotions over time, the poem “ a contribution to statistics” by wislawa symborska suggests that the only unchangeable characteristic is mortality.

the author poses a distinction between the approximate and non-approximate numbers which correspond to our need for certainty in life and the difficulty of achieving it. our efforts to measure the exact often fail because the world is not always clearly structured .the poem seems to imply   that the only thing that is certain and has an exact number is death.  

where is the passage?