As Jesus came down from the mount of transfiguration, he met a man whose son was demon possessed. The nine apostles had not been able to cast out the demon and Jesus rebuked them for their lack of faith. After he had cast out the demon, the nine disciples asked Jesus why they had not been able to do so. Jesus replied, "This kind cannot be driven out by anything but prayer.” (Mark 9:29). [Peter, James, and John were on the mount with Jesus and had not failed, or even tried.]
Despite the popularity of this movie genre, demons do not possess people today just as they did not do so in the Old Testament. Demons operated for a short time to show the power of Jesus to control them. The only Old Testament passage to use the expression "unclean spirit" which is found so often in the gospels states that they will end in "the day" a fountain is opened for sin (Zech 13:1-2). In fact, neither demons or unclean spirits are mentioned in any of the epistles as possessing people as they do in the gospels and Acts.
Nevertheless, I believe that we are possessed. Not by spirit beings but by decades of sinful habits or by years of thinking evil thoughts so that our minds are grooved into following those paths. Often, when we decide to turn over that new leaf, we find that we cannot cast out these "demons." Just like the nine apostles, we have expected it to be easy. We sowed the wind and find we have a tornado in our soul that we cannot control (Hos 8:7). Neither baptism nor genuine intent to change is a quick fix for cleansing our souls of these sins. This kind comes out only by prayer.
But, a quick prayer when we are already halfway into the situation will not suffice. It did not for the nine and these quick patches on a bleeding wound of the soul will not work for us. And, somehow, I suspect God becomes weary of prayers for forgiveness when there were few or no prayers for strength before we sinned.
Our regret for this habitual sin should bring us to the knees of our heart continually throughout the day begging for strength from the Lord. This earnest care to be pure will have us making time for studied lengthy prayers about our specific sin. Our indignation that Satan still seeks to use the same old weakness against us again must motivate us to learn scriptures to enrich and strengthen our prayers. The fear of God's wrath should have us examining the situations that lead us to fall and praying with zeal to prepare for them. Our longing to be pure before a holy God will lead us to make the time for these prayers, no excuses, no exceptions.
Actual unclean spirit demons may not inhabit humans anymore, but the demons we have created by our careless certainty that God will keep on forgiving can be as hard to cast out. Unless we do, we will not see God.
Set your hope perfectly … as children of obedience, not fashioning yourselves according to your former lusts in the time of your ignorance: but like as he who called you is holy, be ye yourselves also holy in all manner of living; because it is written, Ye shall be holy; for I am holy. And if ye call on him as Father, who without respect of persons judges according to each man's work, pass the time of your sojourning in fear. (1Pet 1:13-17)