Today the Orthodox Church celebrates the memory of St Maximus the Confessor, that profound theologian, confessor of truth, and exemplary monk. Many of his properly theological works – as opposed to his ascetic writings – are notoriously dense and difficult to comprehend, especially in the original Greek. No one, however, should deprive themselves of the Confessor's "symphony of experience," as Fr Georges Florovsky described his works. The very best volume with which to start is On the Cosmic Mystery of Christ, containing an exemplary introduction by the translators, Paul L. Blowers and Robert Louis Wilken, followed by a selection from St Maximus' two main collections of theological reflections: his Ambigua (or Difficulties) and his Questions to Thallasius, along with one of his Christological opuscula.
I will reproduce here (without the notes and annotations) one of the shortest texts contained in this volume, Ad Thallasium 1: "On the Utility of the Passions" (pp. 97-98):
Question: Are the passions evil in themselves or do they become so when used in an evil way? I am speaking of pleasure, grief, desire, fear, and the rest.
Response: These passions, and the rest as well, were not originally created together with human nature, for if they had been they would contribute to the definition of human nature. But following what the eminent Gregory of Nyssa taught, I say that, on account of humanity's fall from perfection, the passions were introduced and attached themselves to the more irrational part of human nature. Then, immediately after humanity had sinned, the divine and blessed image was displaced by the clear and obvious likeness to unreasoning animals.
The passions, moreover, become good in those who are spiritually earnest once they have wisely separated them from corporeal objects and used them to gain possession of heavenly things. For instance, they can turn desire (epithumia) into the appetitive movement of the mind's longing for divine things, or pleasure (hedone) into the unadulterated joy of the mind when enticed toward divine gifts, or fear (fobos) into cautious concern for immediate punishment for sins committed, or grief (lupe) into corrective repentance of a present evil. In short, we can compare this with the wise physicians who remove the existing or festering infection of the body using the poisonous beast, the viper. The spiritually earnest use of the passions to destroy a present or anticipated evil, and to embrace and hold to virtue and knowledge. Thus, as I have already suggested, the passions become good when they are used by those who "take every thought captive in order to obey Christ" [2 Cor 10:5].
What this means is that if Scripture mentions anything about the passions in connection with God and the saints, the following applies: in connection with God, the passions are mentioned for our benefit, revealing the saving and beneficial movements of divine providence accommodated in a way that befits our own experience; with reference to the saints, on the other hand, when the passions are mentioned it is because the saints cannot convey in corporeal speech their spiritual inclination and dispositions toward God apart from human passions.
We see that, according to St Maximus, the passions came into existence following the Fall; they are not an intrinsic part of man as created by God. They are bound up with our lower, carnal, animal nature, but can separated from this corporeal objects and put to good use as a means towards virtue: love and desire can be turned towards God. One might say, adapting the saint's analogy, that passions such as fear and grief can serve like leeches that suck evil inclinations out of us. However, when we speak of God as having passions (e.g., anger or jealousy), this is solely in order to express the inexpressible in terms that we can comprehend. When the saints speak of their great yearning and passion for God, this too, is using human language in a weak attempt to express the divine.
The ascetic effort, then, is not so much matter of repressing the passions, so much as expressing the passions properly, of turning our natural energies away from pleasing our own flesh and towards the love of God. While all of this takes place within the body as the locus of our salvation, it is not expressed sensually or physically. It might be profitable to compare this approach with that of the medieval Spanish mystics, with their "devotion of ecstasy or rapture," which often appears crudely carnal in comparison.
The above image of St Maximus (with his miracles) is an early 17th-century Stroganov school icon from Solvychegodsk.