The devil has also some authority (exousia) in this world (Acts 26:18). There are authorities and rulers of darkness in the heavenly places (Eph.6:12), against whom the Church is engaged in a battle. The authority of the devil is called “power of darkness” (Col.1:13).
These evil authorities have been disarmed by Jesus; so, they have no power over the church. (Col.2:15; Matt.16:18). The child of God is delivered from the authority of the devil and from the kingdom of darkness and is transferred to the Kingdom of Jesus Christ (Acts 26:18; Col.1:13). He is a citizen of heaven and is protected by the forces of heaven (Phil.3:20; Psa.91:11; Heb.1:14). The devil has no authority over the believer (1John 5:18).
However, the world still lies under the wicked one (1John 5:19)
The devil is called the Prince of the power (exousia) of the air, the spirit that now works among the disobedient (Eph.2:2; Job 2:2)
He is called the god of this world or age (2Cor.4:4)
His workings are known as the mystery of iniquity (2Thess.2:7)
The devil will give great power and authority to the Anti-Christ during the 7-year Great Tribulation (Rev.13:2) (He tried to approach Jesus too, but failed (Luke 4:6,7).
But, Jesus will bring the devil and his powers to an end (Rev.17:13,14; 19:20; 20:10).
Sometimes, God allows the devil to oppress His servants; but, God controls the whole event and protects His servants (Job 2:6; 2Cor.12:7; 1John 5:18; 1Pet.1:5; 5:8,9; James 4:7)