The main point of this excerpt is that African-Americans were not considered US citizens.
In the Supreme Court case Dred Scott vs. Sandford, Scott is suing for his freedom from slavery. This is because his master brought him to the Wisconsin territory, a territory where slavery was outlawed.
However, the Supreme Court ruled against him. The reason why they ruled against him is based on the excerpt above. The Declaration of Independence did not make it blatantly clear that slaves were considered citizens. Since they were not considered citizens, they had no legal rights that slave owners had to respect.
They had extremely fertile land and lots of manpower, so it made for profitable business.
Answer:
for us to have rights and be equal to men
