"...to another discerning of spirits" (1 Cor 12:10) The owner of the gifts knew very well that the devil will seek to corrupt the authenticity of the gifts by counterfeiting them. He knew that the evil one will come with gifts resembling the ones He gives. He knew that the seducer and deceiver will try to lure people's heart away from the real gifts by introducing fake ones. Can you count how many people have had their hearts biased or turned away by people pretending to be operating on the gift of the Holy Spirit yet taking advantage of people and ripping them off. Have you not heard of "arranged" miracles? Supposed "men of God" who perform powerful miracles and healing on the crusade ground, only to spend the night on the lapse of prostitutes. People have lost faith in the trueness of spiritual gifts because the fake ones are almost everywhere. This is why the Holy Spirit included among His gifts the ability to discern the spirit behind the manifestation of any gift. If you ask me, this is one gift that every christian should ask the Holy Spirit to bless him or her with. Perhaps the most important warning the Holy Spirit gave the church was "believe not every spirit, but try the spirits whether they are of God" (1 John 4:1) .
Discerning of spirit provides supernatural insight into the realm of the spirits. It reveals the kind of spirit that is acting in a person who is manifesting a supernatural gift at the moment the manifestation is going on, not after. We must note that what the Holy Spirit gives is the gift of discerning of spirit, not the gift of discernment. There is no such thing as the gift of discernment. Discerning of spirit is not some kind of spiritual mind-reading; it is not psycho-analyses. It is purely a supernatural revelation of the spirit behind any manifestation of spiritual gift. The gift is not learnt or trained. It is automatic and operates by faith in the Holy Spirit.
Now, there are three kinds of spirit, namely: divine spirit or the spirit of God; satanic spirit or the spirit of satan and human spirit or the spirit of man. Now discerning of spirit is the ability through the Holy Spirit to supernatural know which of these spirit is at work in a person at any point in time.
The uses of the gift of discerning of spirits include: to discover a servant of the devil, to help in checking the plans of the devil, to expose plausible doctrinal errors, to unmask demonic miracle workers as shown in the following scriptures Acts 13:9-10; Acts 16:16, 1 Tim 4:12, 2 Pet 2:1, 2 Thess 2:9