As a teacher, I tend to allow students to sit where they want at the beginning of a semester; the reason is I want to know something about their character. Friends find one another; friendships are based on likeness of character. Students of like character sit together: "criminals" find one another, the "brainers" find one another; and students of genuinely fine moral character find one another. It's the opposite of what we know about magnetism: two positively charged objects repel one another, and two negatively charged objects repel one another. But when it comes to moral character, like attracts like. Somatic narcissists can walk into a room of partiers, look around, and immediately distinguish who it is they can seduce from those they know they cannot seduce; they can very quickly pick out those who are needy, who have such a desperate need to be loved that they'll fall for any line.
All this has to do with self-knowledge; we know ourselves from within, and because of that, we know those who are like us, for we recognize them just by the look in their eyes. This is true on all levels of human cognition. When a dog yelps and reacts quickly when a child steps on his foot or his tail, we know this to mean that the dog is in pain only because we know ourselves from within - I yell and react violently when someone steps on my foot. Accompanying every awareness of an object outside of me is a subjective knowledge of myself as knowing that object - I know that I am knowing something outside of me. If we did not possess this self-knowledge, the dog's yelp and his sudden reaction would be unintelligible to us, a veritable mystery.
Why is it that the sheep hear and recognize the Shepherd's voice? The reason is that the Shepherd lives inside them. If Christ lives in you and speaks in you, then you will recognize his voice outside of you. Jesus says in the book of Revelation: "Behold, I stand at the door and knock. If anyone hears my voice and opens the door, I will enter his house and dine with him, and he with me" (3, 20). Of course, he's referring to the door of the heart.
If someone is a true prophet, that is, a genuine mouthpiece of God, you will recognize it immediately, but only if you know Christ's voice from within you first, and you will know his voice from within you only if you have allowed him into you. If you are not familiar with the sound of his voice within you, then you will not recognize his voice outside of you.
Allowing Christ into us, however, is not something that is completed on a one-time basis. We allow Christ into our lives by degrees. Only Mary said 'yes' to God completely; for the rest of us, our 'yes' is incomplete and very imperfect, and the spiritual life is about gradually perfecting that 'yes'. So, to the degree that you and I have allowed Christ into ourselves, to that degree we will recognize his voice. Which means there is a real possibility that we will mistake the voice of another for the voice of Christ. In short, we may allow ourselves to be deceived by a false prophet.
I believe it is possible for a non-Christian to recognize and delight in the voice of the Shepherd. Jewish comedian Jackie Mason had a tremendous admiration for Pope Benedict XVI; he saw him as a genuinely good and holy man. Many of my own Hindu or Muslim students delight in the teachings of Christ and the fundamental truths of morality. It is also possible to be a Catholic and to come to Mass week after week and not recognize his voice, but to mistake another voice for his voice. In other words, we can pray our way away from God; we can make the effort to come to Church every week precisely in order to deceive ourselves.
Self-deception is an interesting phenomenon. How it works has been the object of study for a while now. The best explanation I have encountered argues that it works by erecting different confidence thresholds. Think of the threshold of a door; some are high, and some are low. If I don't want something to be true, I will erect a very high confidence threshold, which means I will demand mounds of evidence before I allow myself to be swayed by the claim; if I want something to be true, I will erect a low confidence threshold, requiring much less evidence for me to have confidence in the claim. I have noticed this in myself over the years: if I read about a study that seems to prove something I don't want to be true, I'll demand far more evidence before I trust the study, but if I read of a study that confirms what I already believe, I tend not to demand further evidence, but readily trust the study. It is a double standard that is hard to overcome, even after teaching about it for many years.
An entire culture can be self-deceived, as well as a nation, or a congregation; and it is very difficult to know whether or not we are part of the self-deceived. The way out of this group-think is to make sure you love truth more than you love yourself. Of course, Christ is Truth; he said it himself, so if we love Christ more than we love ourselves, we lessen the likelihood of belonging to the self-deceived, that group which confuses the truth with what they want to be true. But the difficulty here is knowing whether I really love Christ as much as I think I love Christ. Maybe I am deceived about that. Perhaps I believe I am much holier than I really am; and if that is the case, it is very possible that those people I admire most and regard as genuine prophets are really only admired by me because they agree with me. It is very possible that I confuse the worship of Christ with the worship of myself.
I wonder about this in all sincerity, and I include myself in this first and foremost. It's not enough to consider oneself orthodox to be in the safe zone. I've been faithful to Church teaching from as far back as I can remember, but I don't like looking back on my past, because I don't like what I see. I don't like being reminded how many times I've been wrong, or self-deceived.
I think the best we can do is to constantly pray, to get to Confession regularly, to grow in a love for the Eucharist, and to always remain open to the possibility that we are deceiving ourselves. If we are too sure of ourselves, too confident, we won't grow that much. But if we remain open and keep in the forefront of our minds that our glory is not intelligence, but humility, then we keep the way open for continued growth in the spiritual life and a greater ability to recognize the voice of Christ outside of us.