“The great dragon was thrown-down - the ancient serpent, the one being called the devil (greek diablo/accuser) and Satan/opposer, the one deceiving the whole world - he was thrown-down to the earth. And his angels were thrown-down with him.
And I heard a loud voice in heaven, saying — Now the salvation, and the power, and the kingdom of our God, and the authority of Messiah has come, because the accuser of our brothers/sisters was thrown down, the one accusing them before our God by day and by night.” - Rev.12:9-10.
So why is diablo/the devil still allowed to raise havoc upon Earth??
In Eden God included a visible option of straying/imperfection - which was a true possibility once He endowed thinking and reasoning ability. And I guess why do that if you don’t let it run its course!
Obviously He is creating beings “of heaven and earth” - where “He will TABERNACLE with mankind upon Earth made anew” (i.e. Re-Genesis, Rev.21:1-5; 2Pet.3:12-13; Eph.1:10; Col.1:20). But! The whole has to understand good from evil, which is also blessing from curse, or that is, blessing from a virtual abyss of possibilities. And which is also Life from death, because God Most High iS Life, and “is perfect” (Mt.5:48) so straying/imperfection can only ever result in trouble (tribulation), ruin (apocalypse, both individual and collective) and death (not being). So straying/imperfection is really only utterly futile, and this sometimes sad, and even perilous, journey/lesson is unavoidable.
And, there’s this - because God is Life, He lives through, and experiences, all sufferings and sorrows that ever occur. Along with every battle of every war.. every horror ..every murder.. every affront. Why would He put Himself through all that!? So we (angel and man/woman) can have genuine thinking, reasoning, pondering and dreaming ability..?