The two quotations that best illustrates the principle of Federalism are:
"The powers not delegated to the United States by Constitution are reserved to the States."
"Full Faith and Credit shall be given in each State to the public acts, records and judicial proceedings (laws and courts) of every other State."
This is because the Framers of the Constitution feared centralizing power within a single governmental institution, so they gave some powers exclusively to the national government, shared some powers with both national and state governments, and reserved some powers only for state governments.