I know deities aren't absolutely required for religion but it is a standard for most of them. Usually a figurehead is the foremost of a group to rally around.
Normally belief structures are derived from various cultural stimuli, usually from family. The family will imprint various beliefs upon the children and depending on the level of freedom of thought allowed the children they may leave those structures entirely or stay within them. Depending on level of exposure to outside sources of course. It's not always a restriction of thought that would have a child stay within the same culture as they grew up in as we are almost always more comfortable in surroundings that we associate with home and family. If you grow up believing that certain things are true and it's reinforced often enough then if you are confronted with opposing information then your first instinct is to react negatively and aggressively. If you have an idea forced into your head often and repeatedly in a short period of time you can become indoctrinated into believing it's true even if you wouldn't have believed such things beforehand, various religions and agencies that aren't religions have used these tactics for centuries with great success.
Variations of belief structures due to migration of peoples over the centuries have caused great turmoil over time which has continued to this day. Even small differences in what is believed or even slight variances in interpretations of the same information have lead to bloodshed.
In short, you get your belief structures from your family and your teachings you learn as a child which can be modified as you grow but in your hind brain most times you would fall back to your basics when confronted with something which opposes you basic beliefs which can lead to negative responses from both parties.
(I'm still pretty sick so this whole thing may not be totally lucid or well written, sorry for rambling if it happens.

)