In the 1957 Stanley Kubrick film Paths of Glory, set during World War I, French military forces launch an attack against German forces entrenched upon a hill. The initial attack fails miserably with heavy losses, and the fire from the Germans is so intense that some units refuse to attack. The French general, viewing the attack from afar, is so upset at the supposed cowardice of the soldiers that he calls the artillery commander and orders him to direct his fire on the French trenches to drive them out. The artillery commander, in response, requests a written order to do so. The general, growing irate, demands the artillery officer open fire any way. Again, a request for a written order is made. Finally, the general hangs up.
The tactic of the battery commander in asking for a written order is a very wise one, and for two obvious reasons: firstly, the general could later deny the order and have the officer court martialed for firing on friendly troops; secondly, the order was an immoral one - the general was demanding the artillery officer shoot at and possibly kill his fellow Frenchmen. If there was a written order, then the situation would change: it would be confirmed that the general had given the order, and the artillery commander could go through with the order with greater sense of accountability.
Christians likewise today have to follow our Lord's command to be "shrewd as serpents" yet "innocent as doves" (Matt 10:16) when it comes to things such as this. From every turn in the pilgrim's trip to the celestial city, they will be attacked by arrows from the enemy in the form of commands from God. Extra-biblical commands and instructions - in the form of divine commission - will assail them. They will demand that they be followed, whether they make such a demand in the tone of a forceful tyrant or a loving mother. They will appeal to our emotions, our ego, our intelligence, our desire for a tradition, and many other facets of our being. They will all, however, say the same thing: "You may have your Bible, but we have something else you need."
Some have often criticized me for always asking, "Where is that in scripture?" I don't say that, however, to be contentious, but because anything we speak of God should comply with the words of God. The model we should follow is that of the prophet Isaiah who, when confronted by those going after mediums and spiritualists for their answers, replied: "To the law and to the testimony! If they do not speak according to this word, it is because they have no dawn" (Isa 8:20). God spoke this word to us first "in the prophets," and finally through His Son (Heb 1:1-2). Anything that strays from these revelations - or attempts to add to these revelations - is outside the frame of God and His special revelation to mankind, and thus should be avoided at all costs.
God, in His wisdom, has permitted His revelation to be written down and preserved, so that the individual believer may have "the wisdom that leads to salvation through faith which is in Christ Jesus" (2 Tim 3:15). The scriptures not only have (primarily) the testimony of God, but (secondarily) the historical and intertextual eyewitness attesting to its validity. Nothing else in world religion has this kind of validity. Any extra-biblical authority, while perhaps having some use in individual circumstances, does not have this same kind of validity. Scripture is God-breathed (cf. 2 Tim 3:16) and springs forth from God to give life, rejuvenation and direction to the sons of God. It gives us no real wisdom and no real dawn. It is simply a dead yoke to be placed around our neck and bring us down.
Anytime any one comes to us with a special "something" which they desire to impart on us and demand we follow, and it does not comply with the words of scripture, or it is separate from scripture entirely, let us take heed to our predecessors within scripture itself, who sought after the word of God and persevered in the knowledge of it. Let us pray to God as the Psalmist: "I shall delight in Your statutes; I shall not forget Your word" (Psa 119:16).