The Holy Spirit Purifies the Mind
Diadochos was bishop of Photiki, a small town in what is now part of modern day Greece. Concerned for the orthodoxy of his flock, he emerged as a clear leader in the mid-fifth century battle against heretical sects coming out of Mesopotamia. His best-known work, On Spiritual Knowledge and Discrimination, was written primarily to rescue from within that heresy those who were there by chance or just misled by the ambiguous discourses of the unorthodox doctrine.
Clearing and purifying the mind is the task of the Holy Spirit alone - just as when a house is being burgled, the spoils can only be recovered if a strong man bursts in and despoils the burglar. Therefore we ought to keep our souls at peace so that the Holy Spirit is welcome there, so that the lamp of knowledge will always be lit - for when it is, the dark and bitter impulses of the devil will be easy to see and they will be reduced to creeping helplessness as they are caught in that holy and glorious light.
This is why St Paul says: Do not extinguish the Spirit – that is, do not sadden the Holy Spirit with evil acts and thoughts, or his light may cease to protect you. Of course the eternal and life-giving Spirit is not actually extinguished: rather, it is the sad turning away of the Spirit that leaves the mind wrapped in gloom and without the light of knowledge.
The mind has a perfect sense of taste that is able to discern and distinguish. When we are healthy, our body’s sense of taste can unerringly distinguish good from bad, so that we desire only what is good for us. The same applies to our mind, as long as it is in perfect health and not disturbed by too many cares: it can very well perceive and desire the consolations that God offers. Through the action of love, it has an unfading memory of their taste, and so it can always seek what is best. As St Paul says: My prayer is that your love may increase and never stop improving your knowledge and deepening your perception, so that you can always recognize what is best.
Diadochus of Photike