"Submit yourselves therefore to God, resist the devil and he will flee from you." James 4:8
What does it mean to resist the devil? First of all you must believe there is a devil or you are powerless to resist him. Believing in the existence of the devil is Biblical. The scriptures talk about the devil in detail and often. If you are still toying with the idea that the devil is just something that the church made up to scare you, you are living in direct opposition to the teaching of the scriptures. You are powerless to stand against the wiles of the wicked one. You can be tossed around like styrofoam in the wind. It is a good thing to read your Bible and believe it.
If you believe there is a devil, then how can you keep him out of your business? It's simple. "Resist the devil and he will flee from you." Now the theology of it.
The devil is a real being and he is in charge of a great many fallen angels which are now demons.
The devil can and will come your way or one of his demons might be in charge of your particular situation.
The devil or demonic activity can come into your life by the demon spirits barging in or by invitation.
The devil/fallen angels and or demon spirits do have some power, but he/they are not all powerful, nor are they able to be in more than one place at a time, nor are they able to do more than one thing at a time.
The devil and his emissaries are spiritual beings and they are able to interfere with the affairs of mankind in spiritual ways. They can come to you of their own accord, looking for someone to devour or they can be invited in by a willing participant in their evil schemes.
Now here's the part that no Christian wants to hear. The devil or demons have the ability to interfere with the lives of Christians just as well as non-Christians. But there are limitations. Christians have power to resist the devil and or the demons if the devil or his demons come on your territory (life/home/children) without invitation. If you recognize that they have infiltrated your personal space, you can resist their intrusion, (which is their invitation for you to participate in some manor with areas of their expertise).
The devil/demons need a foothold to take or even hang out on your territory. If you haven't given them an opening, they can only pass by and taunt you, tease you or tempt you. But they cannot stay in your space unless you allow it. They can go and come back and that forever, but they cannot stay and reap havoc unless there is legal grounds for them to stay.
Legal grounds could be many things, but in particular:
You are actively involved in harming others through actions of your own.
You are actively involved in an extra-marital affair while you are married.
You watch and enjoy violent movies/video games.
You are involved with illegal drugs.
You are involved with any kind of sexual perversion.
You are involved with a cult.
Keep in mind this is Christians I am talking to.
For non-Christians all they have to be confronted by and participate with the devil/demons is to breath.
Of course if you invite the devil/demons into your life, they will come gladly and do your bidding.
I hope you understand what is at stake if you dabble with the devil, but if you don't there are no words that I can say that can explain the complications, turmoil, heartache, pain, suffering and misery associated with purposely allowing the devil/demons entrance into your life.
Resist the devil. You can do it. If you are born again you have within you the ability to live a life that the devil and his demons have no interest in. "...Resist the devil and he will flee from you."