Matthew 16:21-23 From that time forth began Jesus to shew to his disciples, how that he must go to Jerusalem, and suffer many things of the elders and chief priests and scribes, and be killed, and be raised again the third day.  Then Peter took him, and began to rebuke him, saying, Be it far from thee, Lord: this shall not be to thee.  But he turned, and said to Peter, Get thee behind me, Satan: thou art an offense to me: for thou savourest not the things that be of God, but those that be of men. 

It's interesting that Peter speaks as the oracle of Satan when just prior to this, he spoke by the revelation of God.  Every Christian ought to take heed.  It is easy for us to be deceived.  Our own minds are deceitful and desperately wicked. How important it is that we seek the Lord, our God and not lean on our own understanding! It is also important that we hold on to our theologies loosely, knowing how easily we can all be deceived.