The difference between Gan Eden before and after the sin of knowledge:[1]
Adam Harishon was originally created in Gan Eden. Gan Eden is the area one receives his reward after his passing. Why then was Adam created in his place of reward, if he was prior to doing the work for which the reward is given? In truth, even Adam Harishon was given a set of tasks to perform while in Gan Eden. The verse states that Hashem placed him there “Leavda Ulishmara/To work it and to guard it.” Chazal state that Leavda means that Adam was given the task to fulfill the 248 positive commands and Leshamra means he was given the task to fulfill the 365 negative commands. [Obviously these Mitzvos contained a different connotation prior to Matan Torah, and the intent is for Adam to fulfill these Mitzvos in their spiritual root, similar to the Avoda of the forefathers.] Now, although Adam was already created in Gan Eden, which is the location of our reward, for Adam this was his natural world in which his Avoda was to take place similar to us being in our world in which our Avoda is to take place, and Hashem designated for him a much higher reward than his current world of Gan Eden. However after the sin, Adam was ousted from Gan Eden and was placed in our world, and now the reward for our Avoda became the Gan Eden that Adam was originally located in, which was his natural world.
[1] Likkutei Torah 54b