Asklemmy

Classes are defined by their relations to the means of production and by contradictions in how society reproduces itself which lead to periodic crisis. Class societies require very complex structures to uphold hegemony of the ruling classes and manage all the crisis and move them in time and space towards other societies or to future generations. Which leads to constant war, environmental destruction, etc and is unsustainable in the long term. Like capitalism needs to expand all the time, which is just impossible on a finite planet and structurally needs to produce devisive ideologies like racism and patriarchy to survive.

A classless society, once achieved, doesn't need all this. Getting there requires a lot of struggle because the ruling class has set up all those structures to protect their privilege. But once we're there, society will actually be way more stable than before. No classes means that structures to uphold hegemony aren't necessary any more. That includes the state, which is really just a weapon in class warfare. Racism and patriarchy aren't human nature. They are constantly fabricated and upheld with huge efforts by the ruling class. Those efforts would be free to build other structures instead. Once that actual connect people instead of driving them against each other. No inherent periodic crisis means those don't have to be managed anymore and society can actually continue to develop sustainably without exploiting to exhaustion natural resources, human minds and bodies, communities and societal bonds and care structures like families.

It's hard for us to imagine, because we're so used to thinking inside class societies. It even forms our anthropology, how we think of other people and our ability to emphasize with them. But future people who live it will have a hard time imagining how it could ever have been different.