On a loosely related question about the nature of the doctrine of Sola Scriptura and external sources of Truth, Jas 3.1 gave an excellent answer.
Since Scripture adequately equips you to correct false doctrine, that
implies it is the standard of truth.
So the point is this: If a person teaches something contrary to
Scripture, they are wrong.
That is not to say that everything outside of scripture is wrong (or
"not from God")... just everything contrary. Therefore we reject any
teaching which opposes what we know (based on Scripture);
This is in line with, for example, the Southern Baptist statement of belief on the nature of Scripture:
The Scriptures
The Holy Bible was written by men divinely inspired and is God's
revelation of Himself to man. It is a perfect treasure of divine
instruction. It has God for its author, salvation for its end, and
truth, without any mixture of error, for its matter. Therefore, all
Scripture is totally true and trustworthy. It reveals the principles
by which God judges us, and therefore is, and will remain to the end
of the world the true center of Christian union, and the supreme
standard by which all human conduct, creeds, and religious opinions
should be tried. All Scripture is a testimony to Christ, who is
Himself the focus of divine revelation.
To the groups that I am thinking of, the idea of continuing revelation isn't necessarily dangerous in and of itself, if that revelation is in accordance with the teachings of Scripture. If God doesn't change, any revelation that comes from Him will be in accordance with what He has already revealed to us.
The problem is, from a Fundamentalist perspective, that many Christians seem to believe that personal revelation is on an equal or higher level of authority as Scripture.
In the words of Spurgeon:
Lots of well-meaning Christians, however, seem to operate with the
misconception that biblical revelation is somehow exempt from the law
of contradiction. They suggest that God's truth can contravene logic
if God is so pleased. They often point to the doctrine of the Trinity
or pit divine sovereignty against human responsibility as evidence
that revealed truth is sometimes contradictory.
But Titus 1:2 tells us that "God . . . cannot lie." Therefore even
God's Word must be in harmony with the law of contradiction. One
clear, unresolvable contradiction would be enough to destroy the
trustworthiness of the whole. That's why the enemies of truth are so
eager to try to prove that God's Word contradicts itself.
A more contemporary preacher, John MacAurthur also addresses this, nothing the disastrous, destructive results of misinterpreted "personal revelation from God".
Put simply, from a Fundamentalist perspective, once a person believes that personal interpretation, personal revelation, or personal anything is equal to, or greater than God's revealed Word, that person can believe in anything they want.
Example: http://www.karenkober.net/karen.html
Karen is one of twelve disciples chosen by God to follow His Son,
Yeshua. Called into the desert in May of 2003, she committed to God
for His Son. Upon the commitment, God gave her the Nine Gifts of
Discernment. John the Baptist told her, "As I have opened the path
for Him to come, you are to open the path for Him to come again.".
She is to create a Sacred Garden for Yeshua and His Mother to welcome
the masses. She is to spread the word around the world of His Second
Coming. Yeshua will be seen to her right and the Blessed Mother to
her left. Those with spiritual eyes have already seen Mother walk
alongside of Karen. About 2000 years ago, Maria, Mariamene and
Salome/Miriam walked with Yeshua. Karen was the "Third Mary" at the
cross.
I know this woman personally, although I cave been out of contact with her for several years, I can attest that she believes this, as well as all the other stuff on her website to the very core of her being. She didn't always believe these things. She believes them now because she rejects Scripture as "man-made", and also because "God revealed these things" to her personally. No amount of logic, reason, or Scripture can make a dent in her unshakable faith in the things that have sprung from her own imagination.
It's the perfect example of what is spoken of in Romans 1
Romans 1: KJV
21 Because that, when they knew God, they glorified him not as God,
neither were thankful; but became vain in their imaginations, and
their foolish heart was darkened.
22 Professing themselves to be wise, they became fools,
23 And changed the glory of the uncorruptible God into an image made
like to corruptible man, and to birds, and fourfooted beasts, and
creeping things.
From a Fundamentalist standpoint, this is dangerous to her because the embrace of such anti-Christian beliefs means that she will never put her faith in Christ alone. Her faith is in the "God" that she has created in her own mind. On a personal level, this breaks my heart. And she is actively leading others to follow her, which is dangerous to them as well.
Her beliefs sprung from a belief in God. She believed in Jesus. (Still does, just not the Jesus revealed in Scripture, but rather one she's invented.) But she believes that her own personal understanding, and that the revelations that God gave her are of higher trustworthiness than a Bible that was "made up".
This is where, from a Fundamentalist point of view, personal revelation is distrusted, and seen as dangerous. Not because we believe God can't and doesn't use personal revelation. In point of fact, we do believe that God speaks to us through personal revelation:
- We believe He speaks to us in prayer (perhaps not audibly, but by giving us comfort when we are in His will, and allowing us to sense when we are not - be it unease, uncertainty, etc.)
- We believe that He reveals His will to us in many ways.
We just believe that God will not contradict Himself, and that any personal revelation absolutely must be measured using the plumb-line of Scripture. The danger comes from refusing to check the personal revelation against that plumb-line, and falling into all sorts of false doctrines.
Failure to test personal revelation is a failure to apply 1 John: 4:1 (KJV)
Beloved, believe not every spirit, but try the spirits whether they
are of God: because many false prophets are gone out into the world.
This leaves us wide-open to Satan's lies. He can be pretty convincing, and Scripture warns us that he can disguise himself as an angel of light in order to deveive us in 2 Corinthians 11:14
And no marvel; for Satan himself is transformed into an angel of
light.