Matthew 16: 15 - "Who do you say I am?" This actually occurs in Matthew, Mark and Luke, but this passage leads to the second critical question as well.
This is the first of four critical questions to ask yourself when evaluating anything really, but most importantly, when attempting to discern the motive and validity of someone's teaching or to check your own interpretation of a portion of the Bible.
For example, your typical prosperity gospel televangelists (names withheld to protect the stupid, you know who I'm talking about though) make the error of selling God to be a weak-willed panderer trying to convince people to follow him by promising them money, health, the ability to fly, etc. For those of you that believe that, go back and read the book of Exodus where God strikes Egypt with plagues to see that God negotiates from a position of strength, not pandering.
To quote John Hagee, "God isn't up in heaven saying 'Let's make a deal.' God is up in heaven saying 'This is the deal.'"
This actually hits home for me personally. Whenever I hear someone stating that you have a right to claim wealth or health as a child of God, I think of my mother who has RA. God explicitly told her that He will not heal her because He uses the disease to keep her humble. I also think of my uncle, not a real uncle but he was certainly family. He died to colon cancer in less than a year despite being the most godly man I ever knew.
This is not to say that miracle healings do not occur. I have seen them with my own eyes. But such healings are never under the complete control of the healer. They are always subject to veto of God. Anything less than that strips God of His sovereignty.
Peter answered the question properly. In response to the proper answer Jesus stated that "on this rock I will build my church and the gates of Hell will not overcome it." If the message or action or belief or whatever supports the character of God, then it is most likely going to be true and applicable. You'll still want to continue with other 3 critical questions though to make sure you didn't get it wrong. If it does not, it needs to be discarded because it only cause you problems.
Ted Hanson is author of the Bible School of Hard Knocks http://www.bibleschoolofhardknocks.com which is your source for hard-hitting, relevant Bible study with a rough, "hard knocks" edge updated daily. Learn the un-common sense critical questions to ask and hard knocks rules to cut through the crap and get to the useful material. http://www.bibleschoolofhardknocks.com