Today is the feast of St. Juan de Yepes y Álvarez, better known as St. John of the Cross, Doctor of the Church. From his work of mystical theology, The Dark Night of the Soul (Book I, Chapter II):
As these beginners feel themselves to be very fervent and diligent in spiritual things and devout exercises, from this prosperity (although it is true that holy things of their own nature cause humility) there often comes to them, through their imperfections, a certain kind of secret pride, whence they come to have some degree of satisfaction with their works and with themselves. And hence there comes to them likewise a certain desire, which is somewhat vain, and at times very vain, to speak of spiritual things in the presence of others, and sometimes even to teach such things rather than to learn them. They condemn others in their heart when they see that they have not the kind of devotion which they themselves desire; and sometimes they even say this in words, herein resembling the Pharisee, who boasted of himself, praising God for his own good works and despising the publican.
In these persons the devil often increases the fervour that they have and the desire to perform these and other works more frequently, so that their pride and presumption may grow greater. For the devil knows quite well that all these works and virtues which they perform are not only valueless to them, but even become vices in them. And such a degree of evil are some of these persons wont to reach that they would have none appear good save themselves; and thus, in deed and word, whenever the opportunity occurs, they condemn them and slander them, beholding the mote in their brother’s eye and not considering the beam which is in their own; they strain at another’s gnat and themselves swallow a camel.