I am actively reading both Charles Williams (the Inkling) and JK Rowling's Harry Potter chronicles - including John Granger's superb 'How Harry cast his Spell'...
when I suddenly realised that Rowling's book, across the whole series, is about the best possible illustration of C.W's distinctive ideas of co-inherence, substitution (including substituted love) and exchange.
It was the following passage, from the end of the first book of the series Harry Potter and the Philosopher's Stone - Dumbledore is speaking to Harry:
Your mother died to save you. If there is one thing that Voldemort cannot understand, it is love.
He didn't realize that love as powerful as you mother's for you leaves its own mark.
Not a scar, no visible sign...
to have been loved so deeply, even though the person who loved us is gone, will give us some protection forever: It is in your very skin.
This is pure Charles Williams! Not that I think it derives directly from Charles Williams - rather it indicates that JK Rowling has independently worked-out the same implications as did C.W. - implications which are orthodoxly, traditionally Christian yet somehow neglected or de-emphasised.
He saved others: himself he cannot save - this was said of Christ, indicating the reality of co-inherence - and the same could be said of Harry Potter.
Throughout the book he is saved from death, again and again, by the love of others - especially by sacrificial love, up to and including acceptance of death for love - such love as a kind of real but immaterial and permanent protection... It is operative even when (as in most instances) 'the person who loved us is gone'.
And in the end, in The Deathly Hallows, Harry demonstrates that as we are saved by the love of others; so it is our task to save - not ourselves but others.
Harry sacrifices himself (allows Vodlemort to kill him) from love of others; and the effect of this act of sacrificial love is seen immediately because after Harrys death and rebirth the pupils, Professors, parents and friends of Hogwarts are rendered immune to the curses and magic of Voldemort and the Death Eaters - there are no more casualties from the Good side in the battle.
So, because of the effects of Harry's invisible love, the evil cannot (for a while, anyway) harm good.
Yet all this happens without the Hogwarts defenders or the death eaters being aware of it - only Harry (and Dumbledore) know what has happened.
So this is love that is real (not a psychological trick, not effective because people believe it is effective - but effective even without awareness) love as a real 'substance', but immaterial...
Rowling's is a description of love that is totally in contradiction to the mainstream one in our society - where love is seen as a type of pleasure; something wholly subjective, one-way and temporary.
For moderns, A loves B, and the love is something happening in A's brain. When the brain state changes, or the brain dies, then love dies and leaves nothing behind - unless it has influenced another brain state, which is equally evanescent.
Indeed the modern cliche idea is that love is a short term brainstorm, maybe pleasurable or maybe miserable - but inevitably disappearing like snow in sunshine to leave no trace. Unrequited or one-way love is seen as pathetic, undignified, a waste of time.
Rowling's is a concept of love that saves - as it saves Snape, an almost-wholly nasty man, but who is wholly and gloriously redeemed by his love for a long-dead woman - married to someone else and who eventually disliked him - and the courage this love enables.
And of course, via Lily his mother (who is long since dead, but not 'gone') Snape's love saves Harry, many times - even despite that at a superficial level Snape loathes Harry (and the feeling is mutual).
Snape is a classic 'loser', in love but not loved; making sacrifices - his whole double-agent life is a sacrifice and he is sacrificially killed by Vodemort; except that this is not mere infatuation but real love, as proved by his sacrifice - hence its effects are real and permanent.
And CW's definition of the worst thing - the exclusion of love - is almost a literal rendition of Dumbledore's and Harry's explanation for Voldemort - a man who deliberately lived without love, and therefore became a kind of demon.
So the Harry Potter books can be seen as an illustration of Charles Williams web of exchange, substitution - people doing the work of salvation for each other - and only indirectly for themselves; this enabled because of co-inherence - that we are members one of another (contain a bit of each other) and unified by Christ (contained by and containing).
Love always working in both directions, and across the divide between life and death.
Love as real, effectual, permanent - the only answer to death.
It is very difficult for modern people to understand 'love' (agape) and how it is central to Christianity.
But the Harry Potter series does not just explain Christian love, it shows agape in operation such that readers can experience it for themselves.
For moderns, Rowling's use of love in her plot is extraordinarily strange (so much of it being love between the living and the dead) and it is remarkable that this very obvious and repeatedly emphasized fact is apparently unnoticed - at least consciously.
Somehow, the fact has eluded secular culture that Rowling's mega-bestselling seven volume book is, at a deep level, a precise and completely unambiguous depiction of agape in action, in multiple acts of exchange and substitution, crossing between this life and the next.