In addition to the visible world, God also created the invisible world, that is, disembodied spirits called Angels. They are also called bright spirits because they always see the light of God's face.
One of these bright spirits had the audacity to withdraw from obedience to the will of God, and through this he lost the light and bliss given to him, became an evil spirit - the spirit of darkness, and was cast out by God from heaven to hell. This fallen spirit is called the devil, which means “slanderer.”