Demons are in a true sense internal to those enslaved by passions. In St. John Cassian’s “Second Conference of Abba Moses,” Abba Serapion relates how, while “still a lad and stopping with Abbot Theonas,” he would hide a biscuit in his clothes and eat it later in secret. When he finally succeeded in confessing his sin, Abba Theonas said, “Without any words of mine, your confession frees you from this slavery.” While Abba Theonas was still speaking a burning lamp came from Abba Serapion’s habit and “filled the cell with a sulfurous smell.” Abba Theonas then said, “Lo! the Lord has visibly confirmed to you the truth of my words, so that you can see with your eyes how he who was the author of His Passion [i.e. the Devil] has been driven out from your heart by your life giving confession” (St. John Cassian, 1978, pp. 312, 313).
The Ladder of Divine Ascent talks of the great battle we must fight to defeat the demon of lust.
After we have fought long and hard against this demon, this ally of the flesh, after we have driven it out of our heart, torturing it with the stone of fasting and the sword of humility, this scourge goes into hiding in our bodies, like some kind of worm, and it tries to pollute us, stimulating us to irrational and untimely movements (St. John Climacus, 1982, p. 183).
These are not just figures of speech.
Before holy baptism, grace encourages the soul towards good from
The more subtle demons attack the soul, while the others hold the flesh captive through their lascivious enticements… When grace does not dwell in a man, they lurk like serpents in the depths of the heart, never allowing the soul to aspire towards God. But when grace is hidden in the intellect, they then move like dark clouds through the different parts of the heart, taking the form of sinful passions or of all kinds of day dreams, thus distracting the intellect from the remembrance of God and cutting it off from grace (Ibid., No. 81, p. 282).
So long as the Holy Spirit is in us, Satan cannot enter the depths of the soul and remain there …. Again, so as to teach us once more that it is through the body that Satan attacks the soul which participates in the Holy Spirit, he says: “Stand, therefore, having girded your loins with truth … (Eph. 6:14–17). When, because of the presence of grace, Satan can lurk no longer in the intellect of those pursuing a spiritual way, he lurks in the body and exploits its
St. Diadochos seems to be contradicting himself – seeming to say that demons cannot dwell in baptized believers’ souls at all, but also talking of their moving through different parts of the hearts of believers. Most probably, St. Diadochos means the deepest part of the baptized believers’ souls. Clearly, however, the demons can “lurk in the body” and attack the soul through the body and can dwell in believers’ hearts at some level. These texts are found in The Philokalia, which shows that they are generally accepted Orthodox teaching.
So, enslavement to passions is a true form of demonic possession, which affects both unbelievers and believers. However, demons cannot inhabit the deepest part of the soul of believers. This enslavement to passions is a worse form of possession than the first form of demonic possession because it is freely chosen.