The thoughts and imagery of the mind often serve as channels through which sin enters into one’s life. For this reason, St. John of the Cross teaches the benefits of purging the mind and memory in “forgetting them and emptying itself of them” (Ascent of Mt. Carmel, Book III, Chapter 6). He lists three benefits of this:
1. In the first place, the soul enjoys tranquillity and peace of mind, since it is freed from the disturbance and the changeableness which arise from thoughts and ideas of the memory, and consequently, which is more important, it enjoys purity of conscience and soul. And herein the soul has ample preparation for the acquiring of Divine and human wisdom, and of the virtues.
2. In the second place, it is freed from many suggestions, temptations and motions of the devil, which he infuses into the soul by means of thoughts and ideas, causing it to fall into many impurities and sins, as David says in these words: ‘They have thought and spoken wickedness.' And thus, when these thoughts have been completely removed, the devil has naught wherewith to assault the soul by natural means.
3. In the third place, the soul has within itself, through this recollection of itself and this forgetfulness as to all things, a preparedness to be moved by the Holy Spirit and taught by Him, for, as the Wise Man says, He removes Himself from thoughts that are without understanding.
One can go about this by dropping of, and detaching from, unnecessary thoughts and images of the mind – the interior forum of private discourses.
It is necessary also to safeguarding the senses, especially that of sight and hearing, in order to safeguard the interior peace, ensuring that no impure speech or discourse enters or arises out of one’s being.