Do you mean the commandment not to eat from the tree?
To experience material existence--both the happiness and the misery and all the associated sensual snares and pleasures as well as the abstinence, the endless mind games and even to play with toys and have pets and just learn how to love each other in spite of all the misery. So that when we return we are 'all grown up.'
Really, the whole bible thing is simply about the raising of a child no different than we most all do at least one time--only it is in the spiritual that this happens.
All we every do is 'growing up.' Who knows, when this one's behind us there are probably 15 other facets of existence, besides just the three we know, body, soul and spirit.
Maybe God isn't merely triune but centennial--and so we only have to grow up 97 more times after this.
You just never know...