The concept of selective incorporation is primarily important to the 14th Amendment because:
A. It says that all the rights and liberties in the Bill of Rights applied to the states.
Selective incorporation is a constitutional doctrine that ensures that many of the rights and liberties guaranteed in the Bill of Rights are applicable to the states through the Due Process Clause of the 14th Amendment. Rather than incorporating all rights at once, the doctrine applies them on a case-by-case basis, meaning that specific rights are gradually recognized as being protected from state infringement. Therefore, while option B touches upon the case-by-case nature of incorporation, it does not convey the fundamental importance that selective incorporation has in ensuring that many rights in the Bill of Rights are enforced against the states, which is the key takeaway of option A.