I am surprised that so many self-identified Christians disbelieve in the devil; not only because there are so many biblical references, but also because a devil makes strong sense both metaphysically (in terms of an explanation for the world as a whole) and empirically (as an coherent way of explaining and predicting the specific occurrences of this world).
I commented some time ago that a Christian who was as scholarly, influential and respected as Charles Williams; nonetheless didn't believe that the devil was real.
I found this confirmed in my current re-read of his novel The Greater Trumps, where the character Sybil (who is clearly intended to be the depiction of a very-near Saint - although not convincingly to my mind) says this in her internal monologue:
She did not, in the ordinary sense, "pray for" Nancy; she did not presume to suggest to the Omniscience that it would be a thoroughly good thing if It did; she merely held her own thought of Nancy stable in the midst of Omniscience. She hoped Nancy wouldn't mind, if she knew it. If, she thought as, the prayer over, she put on her other shoe - if she had believed in a Devil, it would have been awkward to know whether or not it would have been permissible to offer the Devil to Love in that way. Because the Devil might dislike it very much, and then...* However, she didn't believe in the Devil...
Elsewhere in the novel in several places, it is clear that Williams regards the most evil thing to be the Ego, the Self; because the characters who are depicted as doing Good are expunging their sense of self of agency, of separateness.
This is a common trope, indeed, among many self-identified Christians through the past 2000 years - I mean that being a "Good Christian" entails a destruction of any recognition of oneself as a separate being from God - the goal is to merge with God, or at least allow God and Goodness to flow through oneself. The self is ideally to become transparent, immaterial - the self standing aside and - eventually - being discarded.
In other words; I am suggesting that among those who regard themselves as Christian but who do not believe in the devil; it seems usual to believe that - in effect - The Ego is the devil.
Sometimes this is even stated explicitly; but even when unstated it seems to be implicit in analysis and discussions of evil; because the attribution of evil tend to converge upon the separate and strong ego of a person - often the separated selfhood of the Christian himself is regarded as the primary evil in the world.
This substitution of the devil by the ego in a context of the primary desire for oneness is, I think, one path by which someone who regards himself as Christian can come to deny the reality of the devil.
This fits with a metaphysical theology that all Good comes from God, and (therefore) for Men to become Good, requires that they cease to offer any obstacle to the shining forth of God's Goodness.
When God is regarded as omniscient and omnipotent, it seems logical that Men can add - from themselves - nothing to Goodness; which is (by definition) already complete and perfect.
Since Men can add nothing to Goodness but only obstruct Goodness by their innate evil; Men should, therefore, ideally become empty, become like conduits for the expression of divine Goodness.
What I am getting-at here is that this is another version of my old bugbear "oneness spirituality" - the only officially- and totalitarian-approved modern spirituality - once again confusing people and masquerading as Christianity.
I tend to think that oneness spirituality is a point of convergence both of Christians who really-believe in in a mono-omni-God with whom the Christian ought to assimilate; and those adherents of 'Eastern religions' (Hinduism, Buddhism) who believe in a more pantheistic and abstract non-personal deity - that is 'everything'.
The conceptual gap is bridged by the soaring abstractions and infinitudes of 'Classical' Christian theology (i.e. using concepts from pre-Christian Greek and Roman philosophy - especially Platonism and Neo-Platonism). In other words; abstractions and infinites applied to God conceptually-merge the person of God into a de facto impersonal deity.
I mean the "mainstream Christian" theology that has, as fundamental, assertions of the Oneness of The Trinity; God's supposed attributes of omniscience, omnipotence, omnipresence etc.; and an infinite gulf posited between creator and created.
What I am saying is that someone who takes seriously, and rigorously pursues the implications of, Classical Christian theology; will find that - one the one hand - he is converging towards a oneness spirituality (and the stance of 'perennial philosophy'); and on the other hand will disbelieve in the devil specifically and the operations of purposive spiritual evil more generally - and will regard Man's self/ego as the biggest spiritual problem in the world.
Both of these are harmful in the context of the spiritual challenges for Christians in 2023.
Firstly, because the Western Christian churches have been corrupted and enlisted on the side of evil; this implies that such a fact will be invisible to one who disbelieves that there is a 'side of evil'.
Furthermore, when the churches are corrupt, the individual Christian must operate from that which is Good in his own self/ ego - as the basis for discernment and seeking spiritual guidance. Unless there is the possibility of recognizing and committing to the Good within us, we cannot discern God's guidance from without-our-selves.
If, instead, we are trying to dissolve our selves into the Omni-God, or into the divine-which-is-everything (it makes little practical difference which); then we are trying to destroy the only thing that might save us in an institutionally-evil world.
*Note: This is a quite extraordinary sentiment for CW to put into the thoughts of a supposedly sanctified woman! To express concern that the Devil "might dislike" something we did, and that this should be considered as a reason for Not doing it!
This suggests either that the devil is not really evil, and so ought not to be made miserable. Or else it confirms that he is being regarded by CW as so certainly unreal; that one may indulge idle fancies about his preferences, and how it might be desirable to 'keep in the Devil's good books...' The "and then..." seems to indicate that unspecified or implied bad things might happen to us, if the Devil regarded us as his enemy.
My interpretation is that Williams may here be hinting (esoterically, to his inner circle - albeit so vaguely as to be deniable) that the Devil does not exist; but that there are personal powers who get called demonic (by many Christians) who can be helpful, of treated with due respect. I would guess that this had something to do with Williams's ritual magical practices.
Of course I cannot be sure; but we do know (e.g. from surviving letters and records of conversations) that this kind of subtle, deniable, esoteric hinting in his published writing was exactly the way he operated.