One of the difficult things about Christianity for a modern convert from atheism is to understand the necessity of Christ.
In this respect my experience recapitulated that of CS Lewis - I could appreciate the reasons to be a theist, to believe in 'god', but I found it hard to understand why Christ was necessary.
It is easy for a modern Westerner to understand how Christ is helpful (e.g. as a teacher) but hard to understand why he is necessary.
And part of the difficulty is understanding 'necessary to what?'. We might accept that Christ is necessary, we might repeat this as an article of faith; but it is apparently difficult for Modern Man to understand just exactly what it is that Christ is necessary to.
What difference did Christ make? - What was the situation before and after Christ - What does the world look like with and without Christ?
Indeed, the problems run even deeper than that, because any answers to the above depend upon a narrative of salvation - relating to God the Father - into which Christ is introduced. So the potential convert finds each question leads not to an answer but more questions - until he comes up against one or another of the fundamental (metaphysical) narratives which underpin Christianity.
Now, most converts do not go through this multi-layered process of questioning, but have a personal and direct revelation of the divinity and necessity of Christ. The problem is for those who do not have such a revelation, or who do have such a revelation but begin to question or doubt its validity (suspecting that the revelation may have been simply a psychological phenomenon due to wishful thinking).
But it is a deep problem for a modern convert when he finds implausible the ultimate metaphysical account of reality into-which the Christian story is being explained. This was my own experience.
As I have already said, a metaphysical account is not necessary to being a Christian; but I found the basic mainstream Christian story told to explain 'why' Christ was necessary, to be a mixture of discordant, implausible and incoherent.
The story I mean is the one about Man's task being to return to a pre-established perfection with the aid of Christ. God created a Good situation, Man destroyed it leading to a fallen world, and Christ restoring the primordial state of Good.
By this account Christ's job was to repair the situation which was set-up by God the Father, and wrecked by Man.
I understand that most Christians throughout history have believed that (more-or-less) this explanation is true - but on the other hand this story is a metaphysical abstraction which has been read-into scripture by a complex process of piecing together evidence from passages here and there, and underpinned by assumptions derived from Greek and Roman philosophy.
What the Gospels seem to be reporting is instead that Christ was operating in a situation where people already knew what was needed, already knew that a Messiah was the only possibly answer to providing what was needed - so that there was already a Christ-shaped-hole in the culture of that time and place. Jesus 'merely' had to demonstrate that he personally was the long-awaited Christ.
But what exactly that 'long-awaited Christ' was, is unclear from the Bible. And the attempt to explain Christ's role in terms of perfection-destruction-restoration has severe weaknesses.
In the first place, it reduces Christ to a role of repair - which does not explain why Christ is primary.
Secondly, it suggests a creator God who was either unable to set-up the situation so that it was robust to a bad choice from a creature whose strengths and weaknesses also had been set-up by that creator.
And thirdly, it is a world-picture that is merely an arc: perfection to wreckage and back to perfection.
It was the basic unsatisfactoryness of this explanation that kept me questioning (against my active will, I should add - I very much wanted to be satisfied with it, tried to be satisfied with it; but met with a continuous gut-resistance); and kept me fundamentally disbelieving of mainstream, bottom-line, metaphysical theology.
And it was this dissatisfaction which kept me seeking, and led to my delight in Mormon theology, when I finally understood that it solved all the above problems, inconsistencies, irrationalities.
For Mormon theology, Christ does not just repair a wrecked situation, he enables further spiritual progression: the whole 'universe' of Mormonism is dynamic rather than static.
After Christ the world does not merely return to where it was, but has had vast possibilities opened-out.
For Mormon metaphysics; the necessity of Christ goes beyond his role in repair and restoration, to enabling a world which is better than the world ever was before.