Writing was the most important in my opinion because it literally showed all of the events big and small that happened in that time period. Most of it's literally written in stone and it's kinda hard to go against someone who was there then.
Cities gave these people a sense of belonging. To be apart of something bigger than themselves which is a basic human desire that everyone needs to fill. It gives them a place safe to grow a family and live their lives.
Government is the law and order. With out it there is anarchy and death and no rules to tell people whats right and whats not. Maybe some of these old leaders saw that so they took leadership to see that the world didn't fall into anarchy.
Art shows the beauty and beliefs that the old civilizations beheld. Clay sculptures and cave painting only scratch the surface of what there is in the world of ancient art.
Social structure made sure everyone had a place. Some of those people may not like their place, but that's just the way that life goes. It made it to also show a sense of belonging.
Religion gave people something to believe. It made them have good hearts in whatever they did. If they didn't do the right thing they believed that the gods would make them suffer and everyone who they love would suffer too.
Specialization of Labor
When enough food was produced to where not everyone had to farm, people found themselves doing a special job to help out their community. This made doing certain tasks go faster since you had to do that job only and you were (hopefully) pretty good at it.