Answer: A. Lincoln shows that the Union was destined to fail because the country chose to allow slavery while claiming national values of freedom and liberty.
In this excerpt, Lincoln is arguing that the cause of the war was slavery, and more importantly, the different ways in which slavery was seen by the government and the South. The government's initial position on it was simply to try to resist its expansion. However, strong measures had to be taken at some point as slavery was not compatible with the values of the country (such as freedom and liberty). As the South was not willing to give up this practice, conflict was sure to follow.