Contrary to the much heard expression, "They have the gift of discernment," there is no such thing as the gift of discernment to mean that one knows things or has insight into given situations. Many people misconstrue 'the gift of discernment' to mean the Word of Knowledge which we have already discussed. The Bible does not state that there is a gift of discernment, but rather it states Discerning of Spirits! There is definitely a gift of the Spirit, an unction from the Spirit of God upon one's being to impart to them the ability to discern spirits in the lives of others. I John 4:1 admonishes us to "...believe not every spirit, but try the spirits whether they be of God...." thus, we can readily see Paul's proclamation of such power in one's life through the Gifts of the Spirit and John admonishing us to use it!
Discerning of Spirits allows us to know whether the spirit of a person is of God or not. There are spirits or demons of many kinds that attach themselves to people, either by oppression (a hovering lingering demon presence that seems to follow you wherever you go) or by possession (an actual entering in of the spirit of demon into one's body and taking possession of an individual, residing within the person and thus controlling him).
There are demons of alcohol, drugs, sex, cigarette smoking, hatred, jealousy, unclean spirits, etc. These spirits take advantage of the works of the flesh cited in Galatians 5:19-21 -- "Now the works of the flesh are manifest, which are these: adultery, fornication, uncleanness, lasciviousness, idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, envyings, murders, drunkenness, revellings, and such like...." A person living in this life without the born again presence of the Holy Ghost living in his heart to war against and subdue the works of the flesh can be approached by the oppressing or possessing power of demon spirits and find himself totally unequipped to resist them -- being in the end result, overcome by them. That person then will reflect the nature of that oppressing or possessing spirit. Many people commit acts of violence, live unbelievably immoral lives knowing that these things are wrong but they cannot help themselves, for they are, "Driven by some power," they say.
'Discerning of Spirits' enables us to identify these ungodly spirits in others, and if they want deliverance and escape from such dark powers, then we can call upon the all powerful Name of Jesus Christ through His shed blood at Calvary and rebuke with all authority, casting the spirits out and away leaving their victims free and fit receptacles for the Spirit of all Spirits, even the Baptism of the Holy Ghost!
The author has been in the presence of great men of God who have walked up to total strangers and told them exactly what kind of spirit they were possessed with and then by the Word of Knowledge told them the exact details of their sinful practices. The stranger being exposed in his sin many times will scream out to God for mercy, while others will walk away being content to remain possessed and live in their sins, loving darkness rather than light, because their deeds are evil (John 3:19). The possessed person must of necessity want to be delivered from Satan -- this, as you can see, would have a great deal to do with deliverance in the life of anyone, for the will of man is an unusual thing. God treats our will as sovereign, He does not transgress our will -- He does not force, though He is ever present to set free. If we will to be bound, then we remain bound. If we will to be set free, then God through the Gifts of the Spirit (and in particular 'Discerning of Spirits') flows through the man of God, and demon powers are exposed and cast out leaving us free!
On one occasion the author can recall being approached by a total stranger in a strange city, and the demon power within the man spoke out and called the author by name, never having heard his name or never having seen him before. The conclusion: the devil knows who the servants of the Lord are but, Praise God, we through 'Discerning of Spirits' can identify the powers of hell and cast them out, rending the chains of hell's emissaries!
We need to try the spirits and see if they be of God or not, and our instrument of detection -- Discerning of Spirits! How great are the ways of God and with what care He has made a ways to keep us safe and secure from all harm within the spirit world. We as born again believers have power to subdue and control the possessed or oppressed. The devil and all his demon powers are ever subject to us through the all powerful Name of Jesus Christ!