You do not understand the scripture. It is because you believe that once you are saved , you are always saved. That is a delusion. Only someone who is in the Lord can expell demons. You of your own volition can not remove demons, they will laugh at you.
You are correct I do believe in OSAS. This is why a Christian does not have a problem casting out a demon. God knows you, the Holy Spirit knows you and demons will know you too.
Paul wants each of us to know that we are in fact a Christian.
2 Cor 13:5 Examine yourselves to see whether you are in the faith; test yourselves. Do you not realize that Christ Jesus is in you. Unless, of course, you fail the test?
It is not wise to A. Approach a demon not being certain that you are in Christ and B. Teach that God is like a human who cannot properly judge our heart and mind as Jer 17:9-11 says
He can and does.
I always cringe within when I hear a Christian say they do not believe in OSAS. Such a silly belief implies that eternal bliss is not possible. As duh a fact 1 + 1 = 2.
The only Christian denomination that can hold to a non-OSAS belief and still keep face are Catholics as you / they also teach Purgatory. But someone like
@backNforth who does not believe in Purgatory would simply teach that God is not so smart, partial and unjust.
Not so smart = Like a human he cannot judge the heart.
Partial & unjust = Person A does what the criminal next to Jesus on the cross did and gets eternal bliss, Person B does this and is used for more by God. Serves Him for fifty years, in year fifty one falls from grace and receives eternal hell.
Both these blocks are ticked / issues resolved if you add a Purgatory. A place where someone who would fall from grace can be re-evaluated.
We see what Jesus tells us, a man who once was in God, who expelled demons, betreys Jesus. The person whose name was once written in the book of life threw it away. He gave it away for a bowl of stew, he betreys Jesus for 30 pieces of silver, he denies Jesus 3 times without seeking the Mercey of Jesus.
1. You say ''Jesus tells a man''. This has absolutely nothing to do with Christianity. At the time of Jesus there was no such thing as a Christian or the presence of the Holy Spirit.
2. All names are in the book of life from birth. Your name can only be blotted out. It does not get written in.
Rev 13:* / Rev 17:8 'written from the foundation of the world'.
3. Regarding exorcisms, I am going to be honest and blunt.
At large the Catholic church does not know the Holy Spirit. It is a word you know of. Not a Being whose presence is
felt and known.
A Christian can sense the Holy Spirit and if they do, there is no such thing as a demon not listening to you. On some occasions you can sense the Holy Spirit not wanting to do something. I have experienced this with miracles and healings. Sometimes it is God's will and sometimes it is not. It is as simple as that.
Now,
many non-Christians 'partake' / 'taste' of the Holy Spirit. They are in some way sanctified by the Holy Spirit. These people will be able to cast out demons and heal the sick on most occasions. Reason being that
the Holy Spirit elevates the name of Jesus beyond all other names. Today using the name of Jesus carries a lot more weight than it did pre-cross / OT.