The entire difference between possession and ownership relates to the moral factor.

When possession was the rule, the concept of right and wrong was not in existence - and certainly not in the sense that we understand it today. 

Might MADE "right".  Any person could have any property in any amount, IF he was big enough and strong enough to hold it, and to prevent others from taking possession of it from him.

Under such circumstances, an individual could not make a decision concerning his or her property, and expect it to be meaningful or adhered to in his absence.  His physical presence (if not actual grasp) of the item was the necessary and deciding factor.

Under conditions of increased available property through increased production, it was quickly found that mere possession was impractical.  The amount of property that any person can physically dominate and control is very limited. 

At this time the idea and concepts of morality were developed. 

This meant that a man who "owned" something, would be considered the ultimate decision-maker over the property, whether or not he was present.