I'm a bit of a C.S. Lewis fan and have read quite a few of his books.
One of them, which he said was very hard to write because he had to think from an awkward perspective, was his very popular "Screwtape Letters" .
In this book he had a senior devil, Screwtape, tutoring and encouraging his nephew, Wormwood, in the ways of guiding humans through a life of self-seeking misery to eternal damnation.

Another author has since followed the same idea but given it an interesting extra dimension.
Randy Alcorn, also a C.S. Lewis fan, has written "Lord Foulgrin's Letters" where he likewise has a senior devil, Lord Foulgrin, teaching and supervising an apprentice in the techniques for misguiding humans towards their own destruction.
Alcorn's other dimension is the inclusion (in alternate chapters) of a typical middle-class "family man" with ho-hum marriage, impending affair, miserable wayward kids, corporate job pressures, materialism and consumerism, and all the usual ordinary stuff of daily life.

Foulgrin has his work cut out for him when the man is befriended by a Christian who challenges some of the man's thinking and poses a different perspective. The battle for the soul ensues and the tricks and strategies expounded in Foulgrin's letters makes excellent teaching on spiritual matters.
Alcorn is as orthodox as Lewis, and I have now read many of his critics (both Christian and non-Christian) who will argue this way and that, but agree in unison that he is Scripturally accurate in everything that he writes.
Having already read Screwtape, I appreciated Foulgrin as well.

Why I mentioned this book was that the man in the story, having become a Christian despite all the efforts of Foulgrin and his apprentice, decides he must share the Gospel message with his dying father, a cynical and rather unpleasant person.
Just as he begins to do so, in walks the hospital chaplain who is of the type that has a watered-down faith such that he is completely insipid and useless, indeed dangerously worse. He says supposedly reassuring things about everyone going to heaven regardless, that "there is a little bit of Jesus in everyone" and other such weird euphemistic non-Christian notions.
Of course the father latches on to all this and uses it to stop hearing the truth, while the namby-pamby lukewarm minister smiles benignly and reassures everyone that God is love and that is all that matters. He makes Jesus into a complete non-issue, Foulgrin having the minister well under his thumb.

Since beginning to read the Bible more critically for myself in the last couple of years, I have discovered so much of that which I was taught was not always Scripturally accurate, and much that did have a significant bearing on things was simply left out.

A classic example is the standard "God is love" without the all important "God is righteous and holy" and what ramifications that has in combination, each one on the other.
I had decided it was completely unfair that God should hold us all responsible for what Adam and Eve once did – after all, we had not even been born! - and if he was also a just God, as is so often claimed, then that simply couldn't be so. He would naturally love us too much not to welcome us all into heaven, no matter what, let alone condemn us for something someone else did long before we were born.
It was C.S. Lewis and his exposition of moral guilt in another book "Mere Christianity" (together with some help from my friends) that suddenly made sense of it for me.
It should have been made to make sense way back in the very beginning, except that the unqualified "God is love" and "therefore everything will be fine regardless" message (which makes Jesus, his crucifixion and resurrection, largely irrelevant) was the one that I had been given instead.
That was certainly not the message of the Jesus in the Bible.
And as one of my friends pointed out, if you don't regard the message of that particular Jesus, then you can have any Jesus you care to imagine - but he just won't be the same one that this whole thing is about.

Oh, and wouldn't Screwtape and Foulgrin both be so pleased!

Read more:
Lord Foulgrin’s Letters
The Screwtape Letters