We are not dealing merely with a battle against the world and a worldly mentality that would deceive us and leave us dull and mediocre, lacking in enthusiasm and joy. Nor can this battle be reduced to the struggle against our human weaknesses and proclivities (be they laziness, lust, envy, jealousy or any others). It is also a constant struggle against the devil, the prince of evil. Jesus himself celebrates our victories. He rejoiced when his disciples made progress in preaching the Gospel and overcoming the opposition of the evil one: “I saw Satan fall like lightning from heaven” ( Lk 10:18).
We will not admit the existence of the devil if we insist on regarding life by empirical standards alone, without a supernatural understanding. It is precisely the conviction that this malign power is present in our midst that enables us to understand how evil can at times have so much destructive force. True enough, the biblical authors had limited conceptual resources for expressing certain realities, and in Jesus’ time epilepsy, for example, could easily be confused with demonic possession. Yet this should not lead us to an oversimplification that would conclude that all the cases related in the Gospel had to do with psychological disorders and hence that the devil does not exist or is not at work. He is present in the very first pages of the Scriptures, which end with God’s victory over the devil. Indeed, in leaving us the Our Father, Jesus wanted us to conclude by asking the Father to “deliver us from evil”. That final word does not refer to evil in the abstract; a more exact translation would be “the evil one”. It indicates a personal being who assails us. Jesus taught us to ask daily for deliverance from him, lest his power prevail over us.
Hence, we should not think of the devil as a myth, a representation, a symbol, a figure of speech or an idea. This mistake would lead us to let down our guard, to grow careless and end up more vulnerable. The devil does not need to possess us. He poisons us with the venom of hatred, desolation, envy and vice. When we let down our guard, he takes advantage of it to destroy our lives, our families and our communities. “Like a roaring lion, he prowls around, looking for someone to devour” ( 1 Pet 5:8).
Gaudete et Exsultate, 159-161