I think it's super interesting that satan has an actual productive and important role in the plan of salvation. Would this whole experience even work if someone wasn't here to test us? Was it actually essential that some should rebel and attempt to lead people away? Like, satan was definitely the one that tested Jesus, but God let him. What if satan wasn't there? Would God have made another way for Christ to be tested? Do we need satan, or any outside influence, for evil to be there. Does evil just appear out of nothing? Calvin and Hobbes explains it well. 
![Do you believe in the devil? | Calvin & Hobbes | Pinterest ...](media/Do_you_believe_in_the_devil!_!_Calvin_&_Hobbes_!_Pinterest_.jpg)
I compare it to a light. Like goodness is like light, and we use a lightbulb to make it. We don't have a darkbulb to turn on the dark to go to sleep. That's my best explanation. 
It may have been inevitable, then, that somebody would rebel, and if nobody would, the whole test would've been unnecessary. That's my best guess. 
Gabriel means man of God. Rad. Turns out he's Noah. Also rad. 
People were called from before the world. God had stuff like that planned out suuper early. Of course Satan was so manipulated as to actually be helping in the expansive plan of Salvation. 
If the saints of God are leaven to lift everyone up, perhaps the Devil is the heat. As much as he wants to burn everything, he just stimulates the servants of the Lord to do what they do. The problems of the world have been compared to the refiners fire, maybe evil caused on purpose is just part of that fire.