It is clear that even real Christians often lack faith in spiritual processes. In theory we all believe that the visible world of human institutions, the world of communications and media, of power and systems; is only on the surface and that the real stuff goes on behind-the-scenes, imperceptibly, by the spirit...
But how seldom we are able to make this real to ourselves - and how often we pin our hopes, and expend our efforts, on worldly activities... How often we measure our success by public, measurable, 'objective' outcomes (such as statistics and surveys, or government and media reports, or what high status people are saying and doing).
Some denominations are very good about emphasising prayer; but this can again become an effort of organisation - with success measured by how many people can be gathered in prayer meetings or in other mass activities; or when the success of such prayer is itself measured by the perceptible effect on public discourse and policy.
This is dangerous, and tends to lead to despair in a world where institutions are deeply corrupted and habitually dishonest, and where the public arena is so controlled.
I think the answer is that we each, as individuals, need to base our understanding solidly on that which we personally know; and know directly by our best and solidest intuitions.
We cannot usually persuade other people of the validity of these personal intuitions - and we should not try to. We should speak, live, work, evaluate, (and especially) think from these intuitions - but not try to 'defend' them using the publicly-acceptable means of 'evidence', 'logic' etc.
An example is miracles. My conversion to Christianity was confirmed and solidified by a few miracles in response to prayer - I have never told anyone about the nature of these miracles because I know that they would sound feeble to a skeptic; and that there are plenty of alternative explanations for them. But I know they were miracles, and I also know that they were meant for me specifically.
Once we start to think this way; we will find that there are many events in our lives that confirm, sustain and increase our faith - but (as a general rule - recognising exceptions) we must not yield to the temptation to try and use these 'spiritual gifts' to convince other people.
We should be grateful for them, and use them in our personal lives, as evidence of how we ought to be living.
Thus we may build-up a solid, sustaining faith in the reality and power of 'spiritual processes'.