The notion of God was created on basis of search of an ultimate Authoritative figure, thus justifying unjustifiable social hierarchies and giving birth to a sacred, unquestionable bloodlines.
Monotheistic religions are directly responsible for most of the human suffering through ages. The bible itself is a strict invitation to accept a suffering as a prime basis for a fucking human condition.
The human condition is just that - human-fucking-condition. It should not depend on any mercy of master, that's called slavery - and a concept of god just abolishes an individual responsibility of direct exploitation, transferring the ownership of the soul to some imaginary authoritarian third party.
Not cool in my opinion.
Religion on a broad scale probably helped us trust and work with one another outside of our initial family, tribal and city groups.
In the smallest social circles, you knew to trust your family and your tribe.
As they grew, you knew to trust your city and perhaps your nation-state.
At some point, society became complex and warranted the need to trust merchants and travelers from other countries and far away lands. This became easier if you knew the guy was catholic/christian/etc. You could then assume a common set of moral values.
Now though, its a crutch we shouldn't need. People are people, most of them are good and trustworthy.