discerning of spirits(v.10)—Satan is the great deceiver (John 8:44) and his demons counterfeit God’s message and work. Christians with the gift of discernment have the God-given ability to recognize lying spirits and to identify deceptive and erroneous doctrine (see Acts 17:11; 1 John 4:1).
Paul illustrated the use of this gift in Acts 16:16-18, as Peter had exercised it in Acts 5:3. When it was not being exercised in the Corinthian church, grave distortion of the truth occurred (see v. 3; 14:29).
Though its operation has changed since apostolic times (because of the completion of Scripture) it is still essential to have people in the church who are discerning. They are the guardians, the watchmen who protect the church from demonic lies, false doctrines, perverted cults, and fleshly elements. As it requires diligent study of the Word to exercise gifts of knowledge, wisdom, preaching, and teaching, so it does with discernment. 
An important gift for the protection of the church is that of discernment, the distinguishing of spirits. The basic meaning of distinguishing has to do with separating out for examination and judging in order to determine what is genuine and what is spurious. Satan is the great deceiver, “the father of lies” (John 8:44), and ever since the Fall he and his demons have counterfeited God’s message and God’s work. All Christians should judge carefully what they hear and read and “not believe every spirit, but test the spirits to see whether they are from God” (1 John 4:1).
That is what the God-fearing and “noble-minded” Jews of Berea did when they first heard the gospel from Paul (Acts 17:11). They tested Paul’s word against what they knew of God’s Word, and because the two words matched they believed that what he preached was from God and not from demons. That is what every believer should do with every message that claims to be from God. No preacher or teacher of the gospel should resent having what he says judged against Scripture.
Those to whom God has given the gift of discernment have a special ability to recognize lying spirits, and this gift is the Spirit’s watchdog. Some ideas that are given as scriptural and that on the surface seem scriptural actually are clever counterfeits that would deceive most believers. Those with the gift of discernment are the Holy Sprit’s inspectors, His counterfeit experts to whom He gives special insight and understanding. The gift was especially valuable in the early church because the New Testament had not been completed. Because of the difficulty and expense of copying, for many years after its completion the Bible was not widely available. The Holy Spirit’s discerners were the church’s protectors.
The gift of discernment is also especially valuable when the church and the gospel are considered acceptable in society. When Christianity is persecuted, counterfeit teachers usually are scarce, because the price for being identified with the gospel is too high. They are much more likely to appear in times and in places where Christianity is considered respectable or at least is tolerated. In parts of the world today, evangelicalism is popular and often profitable. All sorts of teachers, preachers, writers, and counselors claim to be evangelical and biblical.
Although any thinking person realizes that all the ideas cannot be biblical, simply because many of them are so contradictory of each other, it is not always easy to know which are true and which are not. Most often they are a mixture. Counterfeit teachers used by Satan usually have some truth in what they say. Unfortunately, many basically sound teachers sometimes undiscerningly pick up ideas from psychology, philosophy, or popular thinking that seem biblical but are not. It is the ministry of those with the gift of discernment to help separate the wheat from the chaff.
The Corinthian believers who had that gift either were not using it or were being ignored. Otherwise the perverted ideas and practices that Paul deals with in this letter could not have flourished as they did. Discernment is the gift, along with prophecy, that the Apostle urges the Corinthians to use in relation to judging the use and interpretation of tongues. Those with discernment are to judge even those who prophesy (1 Cor. 14:29).
Obviously, the gift of discernment is valuable to the church in assisting Christians to settle disputes among themselves rather than going to court. That seems to be the gift needed by the person Paul speaks of in 1 Corinthians 6, the “wise man who will be able to decide between his brethren” (v. 5).
Even praise of the gospel can be deceitful and misleading. When Paul and Silas began to minister in Philippi, Luke reports that “a certain slave-girl having a spirit of divination met us, who was bringing her masters much profit by fortunetelling. Following after Paul and us, she kept crying out, saying, ‘These men are bond-servants of the Most High God, who are proclaiming to you the way of salvation’ ” (Acts 16:16-17). What the girl said not only was true but seemed to be favorable to the gospel and to those who were proclaiming it.
But the purpose and motivation of what she said was exactly the opposite. The demons who controlled her meant to attract the people and, gaining their trust, then ridicule and undercut God’s Word and the work of His ministers. In that case Paul could not judge by what was said, because the girl’s words were true. He knew she was a demonic instrument only because the Holy Spirit revealed the false spirit that controlled her.
False teaching can be judged by comparing it with Scripture, but false spirits can be judged only by the true Spirit’s gift of discernment. That gift may be called the Spirit’s gift on gifts, because God uses it to reveal to His church whether or not a manifestation of the other gifts is of Him. All imitation of the gifts is not demonic. Much of it is simply the work of the flesh, carnal Christians trying to serve the Lord in their own power and for their own benefit and glory. Summarizing, it can be said that the gift of discernment is given to tell if the other gifts are of the Holy Spirit, if they are merely natural imitations, or if they are demonic counterfeits.
I believe God still empowers some of His people to unmask false prophets and carnal hypocrites. He gives them insight to expose imitations and deceptions that most Christians would take as genuine. The gift of discernment, however, can easily deteriorate into a critical, proud, and self-righteous spirit. It can be judgmental instead of corrective when it is imitated in the flesh. But rightly used it is a great protection to God’s people.
 John MacArthur. 1 Corinthians (MacArthur Bible Studies) (Kindle Locations 1144-1150). Kindle Edition.
 John MacArthur, MacArthur’s Commentary on 1 Corinthians, (Chicago: Moody Press, 1996], 1 Corinthians 12:11.