A Word on Death by Saint Ignatius Brianchaninov
From the introduction.
Getting down to explaining, to the extent of my poor knowledge, of the mere human understanding of created spirits, I believe I should share the teaching about the man's mere blindness that he attained after his fall. Most men are strangers to any concept of this blindness; they are not even aware of its existence! Most men are strangers to any idea of spirits or have one theoretical, most superficial, most intangible and indistinct idea about them that is almost equal to complete ignorance.
In modern human society, mainly in an enlightend society, many people doubt the existence of spirits, many people reject it. Even those who accept the existence of their souls, accept their immortality or their post-mortem existence accept them as spirits, doubt it and reject it. What an awkward mix of mutually inconsistent concepts! If souls exist after they have separated from bodies, than this already means that both good and evil spirits exist. They exist! It is quite clear and obvious to those who began to study Christianity correctly and in detail. Those who reject the existence of spirits inevitably reject Christianity along with that. "The reason the Son of God appeared," the Scripture says, "was to destroy the devils work, so that by his death he might break the power of him who holds the power of death - that is, the devil." (1 John 3:8; Heb. 2:14). If there are no fallen spirits, then the incarnation of God has no cause or purpose.