From my reading this morning by Johann Tauler:

Beware of the False Light
Some people never advance beyond their lower faculties. Their lives are guided solely by natural reason, and the depths of their souls are empty and idle and not formed anew by God. Such people cling to the operations of their own reason as if these were God’s workings in them, but in fact there is nothing in their souls but natural activity. The right exercise of our natural faculties can afford greater joy than all sensual pleasures put together; but if people cling possessively to this joy, they can become most evil and most pernicious.

Here are the signs by which such people can be distinguished; they have not come up along the way of virtue, and they neglect the practices which lead to holiness of life and the extermination of vice. They are filled with love for their own false passivity, false because it is not combined with an active charity, interior or exterior; and they have tried to free their minds of all images before they are ready for this.

So the devil comes and inspires them with sweetness and light which is all deception, and he seduces them so that they are lost forever. He discovers whatever natural inclinations they may have, to unchastity or avarice or pride, and he leads them into such sins. They say that it is God, and not the devil, who has put all this into their hearts, and nothing will persuade them to the contrary; and so the next step in their corruption is “freedom of the spirit,” a false freedom in which they follow whatever their natural inclinations may be.

We should avoid such people more than we fear the devil, because in what they are and what they do, it is very difficult to distinguish them from God’s true lovers.