Why are popular sovereignty and federalism important to the constitution

Popular sovereignty and federalism are important to the constitution because they both say that the people give the government its authority. This principal was important because they wanted the government to be subject to the law not above it.  

We understand popular sovereignty as the concept in which political power rests with the people who can create, alter and abolish government. People express themselves through voting and free participation in government.

And federalism stands for the sharing of power between federal and state government.

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.