How we cite our quotes: (Sentence)
Quote #4
The people were to be left 'perfectly free,' 'subject only to the Constitution.' What the Constitution had to do with it, outsiders could not then see. Plainly enough, now, it was an exactly fitted niche for the Dred Scott decision to afterward come in and declare the perfect freedom of the people to be just no freedom at all. (59-61)
Chief Justice Taney wrote at length in the decision for Dred Scott v. Sandford to convince people that given the historical evidence, the Founding Fathers would not have meant for Black people to be citizens of the United States. Lincoln disdainfully references Taney's interpretation of the Constitution as one that goes against one of the document's (and therefore the country's) basic principles.
Quote #5
We shall lie down pleasantly dreaming that the people of Missouri are on the verge of making their State free; and we shall awake to the reality, instead, that the Supreme Court has made Illinois a slave State. (89)
Remember that Lincoln is giving this speech in Illinois to a group of Illinois, antislavery voters. The northern states have pretty much never wanted slavery to exist there, so creating an image that makes the threat more real his audience would be an effective way for Lincoln to get his audience's attention. This isn't just some far away issue—it could happen to them.