It allowed slavery and found Scott to be property.
Slavery
13th amendment to the Constitution
Scott wasd denied his freedom. The Court interpreted the Constitution to mean that slavery was legal in every state of the Union, because it said a man's property was sacred, and slaves were property.
It was for the court to decide what was correct. And they decided that the Constitution should be interpreted as the Founding Fathers would have meant it. So when they declared that a man's property was sacred, their definition of property would have included slaves.
The Dred Scott decision stated that people of African decent imported to America were not citizens and not protected by the Constitution. The fourteenth and fifteenth amendments nullified that decision.
Because it said slavery was protected by the Constitution.
It declared that slavery was legal in every state of the Union according to the Constitution.
The Supreme Court interpreted the Constitution as it was understood in 1776 - that a man's property was sacred, and slaves were property. This appeared to mean that no state could declare itself to be free soil.
The Court interpreted the Constitution, as they believed the Founding Fathers would have meant. A man's property was sacred. Slaves were property. Therefore slavery was legal in every state of the Union. It added that a black man could not be a citizen of the USA, and could not take a white man to court. So Dred Scott's owners had no case to answer.
It appeared to mean that slavery was protected by the Constitution, and could not be banned from any state of the Union.
Applauded by the South, who thought its interpretation of the Constitution meant that there was no such thing as free soil.
It simply declared that slavery was legal in every state of the Union, because of how the Chief Justice interpreted the Constitution.
In the 1857 US Supreme Court decision that involved the Dredd Scott case, the Court stated the slaves were property and, also, they could never be US citizens. This pro-slavery decision would later require an amendment to the US Constitution in order to abolish slavery.