Multiple times in the movie we see Keller Dover reciting the Lord's prayer. There is little doubt in my mind that the faith-based depiction of evil is intentional. So it was powerful when Dover was sitting outside the room of the man he was torturing - the man he was convinced had kidnapped his daughter - and started praying again.
Our father, who art in heaven
Hallowed be thy name.
Thy kingdom come, thy will be done
On earth as it is in heaven.
Give us this day our daily bread,
And forgive us our trespasses, as we.....................................At which point he broke down. Because he could not forgive the one who, in this horrific act, had trespassed against him.
So this is the essence of the kingdom of God. Jesus came to enable us to do the impossible. Anybody can forgive those they love. But this kind of forgiveness is beyond natural - supernatural - and comes from God.
So how does evil triumph? When we stop short in praying the prayer. Forgiveness - that's where the power to defeat evil comes from.