To the law and to the testimony: If they speak not according to this word, it is because there is no light in them. Isaiah 8:20

This verse is teaching, "To the Bible Alone!" The Bible is God's Word, Law and Testimony. If people do not speak according to this rule it is because they are not saved, there is no light in them. Instead, they are preaching lies from their own, darkened minds rather than the light of the Gospel from the Bible.

But if our gospel be hid, it is hid to them that are lost: In whom the god of this world has blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them. II Corinthians 4:3-4

If anyone uses any means outside of the Bible itself to interpret the Bible, they are NOT bringing the truth of the Bible. This is the sad condition of churches and congregations today as they promote confessions, denominational distinctives and professionalized theology; and as they declare social, economic, political, charismatic and works-based free-will gospels. These are all man-made institutions and aspirations which do not find their source in the Scriptures alone.

Preach the word; be instant in season, out of season; reprove, rebuke, exhort with all longsuffering and doctrine. For the time will come when they will not endure sound doctrine; but after their own lusts shall they heap to themselves teachers, having itching ears; And they shall turn away [their] ears from the truth, and shall be turned unto fables. II Timothy 4:2-4