What

Deliverance is a very prickly subject. Most believers have an opinion about it - sometimes that opinion is based on scripture, sometimes it is based on what a particularly revered speaker says, sometimes it is based on personal experience, and sometimes it is gleaned from popular culture. Regardless, deliverance is real, and something every believer should research. They should do so for at least two reasons.
1 - Demons are real.
2 - Spiritual protection only protects those who engage it.

As a result, there are many people, the world over, under the influence of demons. I would argue, without the Holy Spirit, it is nearly impossible to defend yourself against demons. And here is where it gets sticky. The question is simple - can a believer be under the influence of a demon?

If you believe the answer is no, and you know someone is saved, then you could point to that person and state that they had a relationship with Jesus, thus fully believing they were free from influence. You likely believe that the person, prior to being saved, may or may not have had demons within them, or about them, and upon being saved were freed from the immediacy of the demons. Likely, you also believe that, because the New Testament makes no mention of deliverance where a believer is concerned, that it then can be argued that believers have no real need for deliverance.

If you believe the answer is yes, whether someone were saved wouldn't indicate the presence of a demon, it would merely indicate that the person had more tools with which to fight the demon. You likely believe that the person, regardless of their state, will have demons within and about them, believe that everyone has demons about them, and upon being saved were given the first set of real tools to combat those demons. Likely, you also believe that, because the old testament makes mention of deliverance, and because the Old Testament is the New Testament concealed, that deliverance is very real and for today.

I have my own opinions in this matter, and I don't wish to sway you - what I wish for you to do is truly delve into the matter. I have personally seen too many people delivered, people who were believers, who clearly loved Jesus and were saved, and who were given deliverance, to be convinced that believers aren't under the influence of demons. Likewise, I believe that the whole of scripture is true, thus anything in the New Testament that doesn't quite make sense can often be clarified from the Old Testament, and events in the Old Testament can often be expounded in the New Testament. They are similar messages bound in different parchment but from the same source.

My only true wish is that you pray before and during your quest for information on this subject - I believe this one subject to be so fundamental to a believer's walk that it can dictate whether they truly are freely able to access the Lord's love and walk His path.

Call to action
Research deliverance
Much like selling cars or anything else, the primary purpose of sales is not to sway so much to research. And the best salesmen convince others to purchase from them by providing that research that best exemplifies their point. So your best defense against immoral salespeople is to conduct your own research. Thus, delve into scripture, with prayer, and ask God to reveal to you the truth about deliverance.

Purpose deliverance
Much likely prayer and fasting, deliverance can bring you closer to God's heart. Akin to the reactive deliverance that fasting exemplifies, acting on and realizing proactive deliverance can not only cause a real and sometimes immediate improvement in our walk in Christ but can also gird us against different types of spiritual attack.

Realize deliverance
Once you've researched deliverance and discover who can be its recipients, seek God's will about whether you should be involved in the administration of deliverance. There are billions who would benefit from being freed and released from the demons that sway their decisions, minds, and hearts, have destroyed family lives, and have kept them from hearing and hearkening to God's heart. Being a part of someone's deliverance, and seeing God work the miracle that deliverance is in someone's life is a profound life-changing event.