Today marks the beginning of the season when most people begin to decorate for Christmas, purchase their gifts, and do their holdiay baking, and prepare for yuletide festivities. One of the most popular movies/plays/stories of this season is Charles Dickens' A Christmas Carol. In this amazing tale, Ebenezer Scrooge is visited by four spirits--the ghost of his late partner Jacob Marley and the ghosts of Christmas past, present, and future. Scrooge is full of questions for these ghosts. Some of them answer his questions, while others remain silent. Scrooge asks all of them for proofs and evidences, but in the end, it is Scrooge who is put to the test.
John 4:1-3 (ESV) talks about testing the spirits...but I don't think John was talking about Christmas ghosts.
Beloved, do not believe every spirit, but test the spirits to see whether they are from God, for many false prophets have gone out into the world. By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God, and every spirit that does not confess Jesus is not from God. This is the spirit of the antichrist, which you heard was coming and now is in the world already.
When I was a kid, I used to think that this meant if a spirit appears to you, you should say, "Wait a minute, spirit--let me test you to see if you're legit. Do you acknowledge that Jesus Christ has come in the flesh?" And if that spirit said, "Why, no!" then I'd recognize the spirit to be a demon. But if the spirit said, "Of course I do, you silly boy!" then of course that spirit would be an angel.
Today, I don't think that this is what John really intended. After all, demons are liars anyway--and if such a situation really happened (unlikely), then they'd lie, wouldn't they?
So if this isn't what John intends, what does he mean? 1 Corinthians 12:10 lists "discerning of spirits" among other spiritual gifts of believers. This can mean intuitively sensing the presence of an angel or demon. Or, it can mean the ability to recognize people's false motivations and doctrines.
In this case, John says that any spirit that does not confess Jesus, or acknowledge that He has come in the flesh, is antichrist. (Note--this is not The Antichrist, but simply means someone who purports to be a believer but who is really anti-Christ. See also 1 John 2:18.) Basically, John is saying that there will be many people who claim Christianity, yet whose teachings are far from the truth.
For one, John says that the doctrine of incarnation is essential to real Christianity. After all, if Christ had no flesh and blood, then how could He have shed His blood for us? If there were no body, there would be no resurrection for Jesus or for us.
John also says that a person must confess Jesus in order to be saved. There are a lot of deceiving teachers out there today saying that a person doesn't have to confess Jesus in order to be saved--but that God just saves everybody, whether they believe in Jesus or not. This is far from the truth. 1 John 2:22 (ESV) says:
Who is the liar but he who denies that Jesus is the Christ? This is the antichrist, he who denies the Father and the Son.
Let there be no mistake, John says. Those who reject Jesus are antichrist. Acts 4:12 says that salvation is found in no one else, for there is no other name given under heaven by which we must be saved. God doesn't save anyone just because they're good people, or because He wants to have mercy on everyone despite their rejection of His son. Salvation is for those who confess Jesus as Lord. Anyone who teaches otherwise is antichrist.
Whoever confesses that Jesus is the Son of God, God abides in him, and he in God (1 John 4:16 ESV).
Anyone who would be saved must confess Christ as the Son of God. Don't be deceived. No one is saved because they are an "anonymous Christian" (a "good person" who is outside of the Christian fold). Those who acknowledge that Jesus is the Messiah incarnate, and that He is the Son of God who died for the sins of the world are saved, whether they're "good people" or not. In fact, nobody is saved because they're "good," but because they call Jesus their Savior.
This is what John means by testing the spirits. Make sure that the teaching you receive from pastors and teachers and authors is sound. Don't accept it just because it came from some Christian publishing house or from the pulpit of a church that you trust. Listen carefully in order to discern the truth. And if the message contains error, reject it. This is the discerning of spirits--knowing truth from falsehood. I pray that you'll be discerning of the messages that you hear, and of the messages that you believe.