Dwight,

It seems to me that the things of Matthew 7 work something like this:

Prophecy, exorcism, and the working of miracles are not the fruit to which Jesus was referring when he said that we would know them by their fruit. It's important to understand that miracles do not occur only for Christians and from God. In order to understand this, first understand the nature of a miracle (as I am using the word here): A miracle is a physical effect induced by a spiritual cause. Or, again, when the so-called "physical world" is influenced by the will of some spirit. Non-christians call all such miracles by the same names. Christians, however, differentiate between such. Miracles of the Holy Spirit (or his faithful follower spirits) we call "miracles." Miracles of unclean spirits we call "sorcery." The distinction is one parallel to our distinction between, for example, "angels" and "demons": all demons are angels, but by separating off a certain subclass of angel, we tend to reserve the name angel for those not members of the distinguished sub-group. Similarly, all sorcery is also miraculous, but we reserve the word "miracle" for those miracles that do not also fall into the category "sorcery." Thus, for example, Moses's staff becoming a serpent is a "miracle" (in the lingo usage), whereas the staves of Pharoah becoming serpents were by "sorcery."

So we see it that prophecy is that miracle by which a person speaks, having heard a message from a spirit. If the message he heard was from an angel (a messenger of God), he is a prophet. If that message he heard was told him by a demon (a messenger not of God), then he is a false-prophet.

We don't have a similar set of class / sub-class lingo for the casting out of unclean spirits. Unclean spirits don't cast other unclean spirits out (that's what Jesus was saying with the "a house divided" speech). Sometimes they'll do a little play for us -- one guy listening to an unclean spirit will do some ritual, and the other unclean spirit will leave with a big show. This is a pantomime designed to lend credence to the false teaching of the would-be "exorcist" -- a calculated effort to lead people astray.

Having said this, we can also see that there are some things that come from God (possibly via his messengers) that cannot be produced or mimmicked by unclean spirits. The first and foremost of these is TRUTH. In fact, this is so crucial that John even advises us to use this as a test for spirits to determine if they are clean or unclean, saying:

This is how you can recognize the Spirit of God: Every spirit that acknowledges
that Jesus Christ has come in the flesh is from God, but every spirit that does
not acknowledge Jesus is not from God. This is the spirit of the antichrist,
which you have heard is coming and even now is already in the world. (1 John 4:2-3)

We see the theme again, this time phrased more pointedly at the question of prophecy, in Revelation 19:10 when an angel says explicitly to John that

... the testimony of Jesus is the spirit of prophecy. (Rev 19:10)

We see again and again (especially from John, but frequently from Paul as well) that "the Spirit is the Truth" (because, of course, he is the spirit of Him who is The Truth). Truth is a better test than other fruit (love, peace, patience, kindness, etc.) because while the Spirit of Truth always produces these fruit, these fruit can be mimmicked by the lies of the enemy by generating appearances of love, peace, patience, etc. where there is none that testifies to the Good Work done when Jesus saved us from the fire.

I would conclude by pointing out that this particular speech by which he points out this whole "fruit and tree" topic by saying, "Watch out for false prophets." Later we see that the behaviors of these people are the working of miracles, casting out of demons, and prophecy. These are all actions of prophets (though not necessarily exclusively in the case of miracles and exorcisms). The key fruit is Truth -- the law of God, the necessity of condemnation, the punishment of death, the atonement of Jesus, the repentence of the believer, the forgiveness of sins, and the participation of the believers in the resurrection of Jesus. From this truth comes all other fruit of the Spirit of God.