Christians already won when Jesus Christ died on the cross and saved mankind from sin. But this now begs the question: Why should Christians still have to fight if Satan and his demons are already defeated?

Answering this question, Jennifer LeClaire writes in an article for Charisma News that people live in a world filled with Satan's fallen angels and God's fallen men.

"The war is on for the souls of mankind. Competing with Jesus, who sacrificed His life to set fallen man free, Satan and his demons strategise to keep God's creation in bondage through deception. The kingdom of darkness is working overtime to keep the blinders on lost souls. Part of the reason we're here is to work toward fulfilling the Great Commission," she says.

As Christians, people become Christ's "ambassadors" of light and serve as witnesses that Jesus is alive despite His crucifixion. Christians have to "wrestle against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places."

The war continues, and Christians should not be complacent about this, says LeClaire. "When it comes to spiritual warfare, the battle often starts in our minds. In contrast, the weapons of Satan are carnal, mighty in our flesh for the erecting of strongholds in our minds—and we're the ones arming him," she says.

This is why it is important for Christians to equip themselves with the truth. When people know the truth, they won't fall for the enemy's lies.

"We are double-minded, speaking the Word of God one moment and the enemy's fear-laced lies the next. The only sure way to enforce Jesus' victory in our lives is to consistently wield the sword of the Spirit," she says.