The following comparisons can illustrate what people are like when their intellect has been lifted up but the love in their will has not. They are like an eagle that soars on high, but as soon as it sees something to eat below, such as hens, cygnets, or even little lambs, it drops like a stone and devours them.
They are also like an adulterous husband who has a whore hidden in his basement. He keeps going back and forth to the top level of his house. Up there in the presence of his wife he says wise things to his guests about faithfulness in marriage, but now and then suddenly leaves to go downstairs and satisfy his lewd desires with his whore.
They are also like swamp flies that fly in a column above the head of a running horse. Once the horse stops, they plunge back into their swamp. This is what we are like when our intellect is lifted up but the love in our will remains below, near our feet, immersed in the unclean desires of its nature and lusting for sensual gratification.
Because people in this state shine intellectually as if they possessed wisdom and yet their will is contrary to wisdom, they are like snakes with scales that reflect the light, or like beetles that shine as if they were made of gold. They are also like the strange light over swamps at night, or from the glow of rotting wood, or from phosphorus.
Some who are in this state can masquerade as angels of light, both among people in this world and, after they die, among angels of heaven. After a brief examination there, however, their clothes are removed and they are thrown out naked. They cannot be detected in this world, because here their spirit is not visible; it is covered over with a mask, like the one a comic actor wears on stage. The fact that they can use their faces and words to masquerade as angels of light is both a result and a sign of the fact that they can lift their intellect almost all the way into angelic wisdom, above the love in their will, as I mentioned before. Since our inner and our outer self can go in opposite directions like this, and because our body is cast off but our spirit remains, it is clear then that a dark spirit can live behind a bright face, and a raging spirit can lie behind soothing words.
Therefore, my friend, know people for what they are, not by their mouth but by their heart—that is, not from what they say but from what they do. The Lord says, “Beware of false prophets who come to you in sheep’s clothing but are inwardly as predatory as wolves. Recognize them by their fruits” (Matthew 7:15-16).
from True Christianity, Section 590