If not, then what? as a metaphysical tool

It is common and perhaps normal for modern people to find Christianity, or indeed any kind of religion or serious spirituality, unbelievable. Although sympathetic, they just cannot make themselves believe it.

This is understandable but a basic error - understandable because from the perspective of nomral modern thought then all religions is unbelievable, and error because this perspective a simply assumes the validity of the metaphysics of modernity.

In practice, nearly all serious reflection, or philosophy, is comparative rather than absolute - or, at least, that is how most people understand and express it. Indeed, to be comparative - genuinely - is a level of intellectual sophistication far beyond that of most experts.

When it comes to the basic assumptions about reality (i.e. metaphysics) this is even stronger; there are very few people who even try to do a from-within comparison of two different sets of metaphysical assumptions. Indeed, the tendency is nearly always to deny that these are assumptions and to assert that the assumptions are an inevitable consequence of observation and experience.

For example, the assumption of 'materialism' or positivism: this assumes that the only real things are perceptible by the five senses (vision, hearing, sight, touch, taste) and amplifications of these senses by scientific instruments (either directly detected or else indirectly inferred - sometimes very tenuously, in practice).

The materialist assumption is that something which is undetectable, unmeasurable, by the sense or scientific instruments does not exist. This is the assumption of all public discourse - in politics, the mass media, education, within institutional and corporate communications etc,

Consequently, all assertions of the reality of non-material entities are known for certain in advance to be un-true - therefore merely need to be 'explained-away' as errors of human psychology. Thus, modern metaphysics divides the world into the real versus the psychological - the psychological is a rag-bag of wishful-thinking, stupidity, deliberate deception, inbuilt biases etc. In practice, psychological causes are imprecisely allocated, because of their unreality - why bother being exact when we already know they are false?

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The materialist assumptions of public discourse are only half the story, however; because there is another metaphysical system which operates simultaneously - and that is the primacy of psychology. This is the idea that although materialism is really-real, it is also trivial or irrelevant and psychology is the most important reality. This is the metaphysics of communism, of political correctness, indeed of mainstream modern politics of all types including supposedly 'right wing' and libertarian.

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Therefore most people operate tow sets of metaphysical assumptions, and switch back and forth between them in an unprincipled fashion - if challenged on one basis, they switch to the other, and deny that they have switched.

If pushed, they will assert that the one arises from, and is linked to, the other - that psychology is rooted-in the material: that such and such material conditions will produce such and such psychological consequences. This is indeed the basis of the mainstream modern morality of utilitarianism - that the goal f politics is to minimise suffering and optimise happiness of the population. But this further assumption is not examined nor defended - it is simply a pseudo-answer to a potentially-devastating question.    

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My point here is that the mainstream modern metaphysics, the basic assumptions from which nearly all modern people judge the world - is hardly compelling, even when regarded in isolation. But when evaluated in a comparative fashion, with the assumptions of religion, the relative weakness is immediately apparent.  

Such an evaluation can only be done by recognising that the basis lies in assumptions, by changing one's assumptions, and then by looking-at-life from that new perspective.

That is a necessary first step, but very seldom done. Only after that step has been done - and the world has been experienced from a different metaphysical base - is one in a position to make a choice between metaphysical assumptions.

On what basis is that choice? Well, there is a level of human evaluation which is non-metaphysical - and it is from that pre-metaphysical level that a choice can be made. This pre-metaphysical, non-theorised level of evaluation could be termed intuition, or gut-feeling, or 'the heart' - or natural and spontaneous common sense... but whatever it is called, it is the bottom-line and basis from-which we can choose our assumptions.

It is on this sense that Socrates was speaking when he asserted that the 'un-examined' life was not worth leading. The ancient Greek philosophers were metaphysicians; consequently they were engaged in exactly the activity I have described above - that is, they were examining, or evaluating, their basic assumptions by exploring from inside, and comparing, their consequences.

Once one has done this, then it is clear that very, very few people have done this; and the opinions of someone who has not done this are not compelling - because they don't know any better but have merely passively-absorbed their assumptions: they are in no position either to critique or to defend their assumptions.