For sure, it is believed that evil forces are in existence and it's also believed that thier primary aim is to fight against our success and progress in life. My worried here is, what does it benefit them for fighting against our progress in life? Is it that the success we supposed to acquire in life will now be diverted to them if they successfully barrier such successes from coming to the rightful owners? Or is it just that they dont benefit anything from hindering us the success even though they themselves do not benefit anything from it.

Candid responses pls!

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Evil forces/demons come from satan(the fallen angel), who his purpose in the bible, is described as " he came to kill, decieve and destroy". Our success maybe part of God's plan for us, so he will definitely try to stand in the way against it.
The gain, is to be part of him in the eternal damnation.