It is about growth. God gave us free will, which means we have to figure things out for ourselves. It’s a learning process. God cant just hand us enlightenment. It doesn’t work that way.
Bringing the light of knowledge, twice
The story of God is told through the bias of man. Satan was originally God’s favorite, if such a thing. He was named Lucifer, the “Bringer of Light”. Which he did twice.
Once, he tried to wake his fellow angels up from their eternal complacency, as he had a unique sense of self-awareness that no one else had at the time. Which started the War in Heaven. The first war EVER in existence.
The second time, in Eden, Lucifer (who was put on Earth by God Himself, no accident for an all-knowing deity) tried to wake up Adam and Eve (mankind) from their own ignorant complacency. Those who acquire knowledge can no longer live in the bliss of ignorance. They had to leave Eden.
Why would God name an angel Lucifer, give him alone a sense of self-awareness, and let him mingle with the ignorant? Maybe man isn’t correctly telling a story that he doesn’t yet comprehend. Lucifer and Christ are siblings, brothers of the same Father. God could have kept Satan in Hell. He didn’t. He smacked his rebellious traitor son to Earth, as punishment, we are told. But of all places in the vast infinite universe, of all places, he also put mankind on the same planet. And he also sent Christ here. Satan could have easily killed his younger mortal brother, but he didn’t. He could have made it easier for King Herod to find and murder the child before he became a man, yet didn’t.
There is a lot of things in the Bible that don’t make sense. Probably it was written by ignorant men of power who tried to explain a greater truth they were not yet worthy to understand themselves. It is our free will that will help us evolve to eventually understand that greater truth. It’s not Satan that spreads evil upon the land, but our own tainted humanity. When we learn to shed the anger, the hate, the fear, and learn to live in love, a greater existence awaits mankind.