Then [Jesus] asked him, “What is your name?” And he answered, saying, “My name is Legion; for we are many.” Mark 5:9
Many expressions in contemporary culture have their origin in the Bible—like the expression, “Clothed and in his right mind,” referring to a person who is acting sanely, normally. The words come from Mark 5:15, referring to a crazed man who Jesus delivered from the power and influence of demons. After his deliverance, the man was found “clothed and in his right mind.”
The New Testament takes the existence of demons as a fact, not a fantasy. Jesus drove demons out of many people resulting in their being made well or whole again. The crazed man Jesus delivered from demons was so “demonized” that there was a multitude of demons dwelling in him. When Jesus asked the man his name, the demons answered, “Legion; for we are many” (Mark 5:9)—a legion referring to a Roman military unit of six thousand soldiers. The truth then, and now, is that demons have no power or authority in the presence of Jesus.
The best defense against demonic influence is to live clothed in the full armor of God—the life of Christ Himself (Ephesians 6:10-18).
There is nothing holier, or better, or safer, than to content ourselves with the authority of Christ alone. John Calvin