There is a common line of argument in Christian theology - which is rooted in the 'omni' conceptualization of God as creating everything from nothing (ex nihilo) - which concludes that evil is necessarily irrational, i.e. evil makes no sense even from its own perspective.
(This is sometimes extended into asserting that - therefore, sooner or later - all Men will 'come to their senses' and choose salvation; even those who initially choose hell or are sent to hell.)
But I regard this as mistaken: partly because its premises (omni-God and creation ex nihilo) are wrong; partly because it fails to acknowledge a core aspect of Christianity - specifically, which is that it is an 'opt-in' and chosen religion; and partly because it fails to grasp the potential rational appeal of evil.
To be Good is to affiliate oneself with God's will and creation; evil is to oppose this.
To be Good is to desire to live in harmony with God and God's wishes and with other Beings who have made the same choice; to be evil is to set oneself against creation (and, usually, of other Beings).
But why oppose creation? There might be several reasons that are rational - one is to resent the fact that God created thus, and not otherwise - and with these aims and not others.
Such resentment comes from our-selves as free agents, as (eternal) Beings who have our own wills and creative potential. Evil may therefore be rooted in a conviction that 'I' personally disagree with God, 'I' dislike Gods plans and methods; and 'I' therefore refuse to affiliate-myself with God's work.
Such resentment amounts to a preference for 'myself' over God (despite that this is God's created reality - indeed perhaps exactly because 'I' am compelled to dwell in God's created reality).
Consider: whatever the nature of my disagreement may be, the disagree-er nonetheless finds-himself already-within God's creation.
Evil amounts to a preference of myself (and my desires and motivations) above God and this world he made, including the changes God made to me - without asking for my agreement!
Thus evil is correctly described as a form of pride - of regarding oneself as The Being who ought-to-be God.
So far this might be a purely private 'preference', as leading merely to opting-out of God's creation. In theory a Man might disagree with God's reality, and simply desire not to be a part of it...
But in practice, much evil is also fuelled by resentment against God.
Because he cannot do what God has done; because he cannot' replace God - the evil Man (or other Being) develops an active dislike of God and divine creation...
Because he knows that he cannot replace God, he reacts by the desire to destroy creation: the desire to destroy all that God has done and is doing; simply because it is not what he personally would have chosen to do.
To be Good is to desire to live in harmony with God's creation and the other Beings who themselves have chosen to live in harmony with God's creation.
To be evil is rooted in disagreement with this ideal of harmony; and to take up an attitude of opposition to God and creation - mostly including an attitude to other Beings that regards them as instruments of this opposition (because there is no reason to desire harmony with them), and the desire that other beings with will enlisted to one's own assertion as the legitimate creator.
(Hence the manipulative and exploitative - 'means to the end of destruction' - attitude to other Beings that is characteristic of evil - albeit perhaps not universal... I could imagine an evil that was group-based, rooted in an arbitrary preference for a particular group of Beings - who then manipulate and exploit the other Beings)
I infer from this way of understanding; that evil is, at root, a personal response to the facts of God and creation; and that evil therefore need not be irrational, nor need it be self-correcting.
I assume that some Beings (i.e. Men, Angels/ Demons, and indeed any other of the many Beings of which reality is constituted) may choose to adopt evil as their basic stance concerning God and divine creation.
This ultimate choice to oppose God may be based on a genuine understanding of reality; and evil may therefore be an irreducible preference and choice of perspective - which means that such evil is both rational, and also potentially eternal.
