Lincoln identifies the central dispute behind the secession crisis as a fundamental disagreement over slavery. One section of the United States defended the institution and sought its expansion into new territories, while the other regarded it as wrong and opposed its further spread. The conflict therefore concerned both moral judgement and national policy.

The statement does not treat the two positions as equally valid. Elsewhere, Lincoln consistently opposed the extension of slavery, although at the time he did not claim federal authority to abolish it within states where it already existed. Here, his immediate purpose is to state clearly why ordinary political compromise had become increasingly difficult.

The quote shows how a disagreement over a basic institution can divide a country when each side believes the other threatens its principles and future. It is useful for understanding the sectional tensions that shaped secession and the beginning of the American Civil War.