Notice the demon in today's Gospel refers to himself in the plural. “What have you to do with us, Jesus of Nazareth? Have you come to destroy us?” (Mk 1:24).
When we are not in union with Jesus Christ—when we are separated from him—we are divided internally. We eventually disintegrate.
Practicing our Catholic faith unites us. Our faith makes us whole, or holy. Saint Paul writes in our second reading, “I should like you to be free of anxieties” (1 Cor 7:32). What's one way to be combat anxiety? Pray and have a relationship with God!