The fact of sin makes salvation necessary. All humans need the deliverance God offers through Jesus Christ. Jesus has won the victory over Satan. All believers have a part in that victory. We need not fear Satan and his demons.
Evil is always subordinate to good.
God's battle with evil has been fought and won, but our struggle continues. We still have to face temptations and trials. Our best defense against evil is a right relationship with God through the application of Christ's atoning blood to our hearts and minds. As Christians, we live in two ages at once. Our salvation and God's kingdom is already here, but not yet in its fullness.