It might surprise you to learn that many people do not believe in the devil. Even some Christians deny that Satan is real. Oh, sure they believe in evil, but they think that evil is just a product of bad human judgments.
They are profoundly wrong.
Brothers and sisters:
Draw your strength from the Lord and from his mighty power.
Put on the armor of God so that you may be able to stand firm
against the tactics of the Devil.
For our struggle is not with flesh and blood
but with the principalities, with the powers,
with the world rulers of this present darkness,
with the evil spirits in the heavens.
Therefore, put on the armor of God,
that you may be able to resist on the evil day
and, having done everything, to hold your ground.
So stand fast with your loins girded in truth,
clothed with righteousness as a breastplate,
and your feet shod in readiness for the Gospel of peace.
In all circumstances, hold faith as a shield,
to quench all the flaming arrows of the Evil One.
And take the helmet of salvation and the sword of the Spirit,
which is the word of God.
With all prayer and supplication,
pray at every opportunity in the Spirit.
To that end, be watchful with all perseverance and supplication
for all the holy ones and also for me,
that speech may be given me to open my mouth,
to make known with boldness the mystery of the Gospel
for which I am an ambassador in chains,
so that I may have the courage to speak as I must.
Satan is real. We defeat him through faith in Jesus, prayer, scripture and reception of the Holy Eucharist.