Personally, I hope it's a gift to humanity as a shield to help protect us from our sun or once we figure out how, to establish a colony on the dark side of the moon (a better, smarter option than Mars in my opinion, IF the moon is safe). 

 I don't think it's safe and I don't think we're getting off earth. But then again, if they meant us harm, we wouldn't still be here, so idk