Question: How do evil spirits war against us?
Answer: You should first of all know, that in the demonic warfare against man, each evil spirit has its role. Every sin takes place either through motivation of or our working together with a certain demon, and every passion is supported by a certain demon.
Thus, the leading demons are eight in number, which are as many as the deadly passions: gluttony, lust, avarice, despondency, anger, slothfulness, vainglory and pride.
Each evil spirit wars against us and operates in their own way, depending on the passion they support. However, all the demons work together to immerse us in the deepest possible way in the passions and to make us slaves to sin, in order to separate us from God and lead us to eternal death.
Of course, the power of demons is not rampant and their activity is not without limits. They war against us only as much as God allows - and He never allows them to war against us beyond the limits of our strength (c.f. 1 Cor. 10:13). By this our will, our faith and our love for God are tested and refined, but we also give them this right to test us by our negligence, our laziness, our carelessness and, above all, our pride.
Evil spirits war against us in many ways. Which are these?
First, with our impassioned thoughts by which they captivate our nous, darkening it and coercing it to consent to sin.
Second, with the passions within us, which trigger them to stimulate our impassioned thoughts.
Third, with our physical senses - hearing, touch, taste, smell and, above all, vision. Through these, like doorways, they take from the soul various external stimuli, in order to excite our passions and push us towards sin.
Fourth, with other people, through whom they work to persecute us and do us wrong and lure us into sin.
Fifth, with sorrows, suffering and sickness.
Evil spirits war against us in many other ways, but these are the five primary ways. No matter how they war against us, however, they cannot harm us in any way, as long as we have received the Divine Mysteries of Baptism and Chrismation through which we have received the graces and gifts of the Holy Spirit, as long as we have deep faith in God and as long as we struggle to keep His commandments firmly and with courage, with humility and patience, with prayer and fasting, with frequent Confession and frequent reception of Divine Communion.
Source: Excerpt from Απαντήσεις σε ερωτήματα Χριστιανών (Answers to Questions By Christians) by Elder Eustratios Golovanski, 2007. Translated by John Sanidopoulos.