This struck me as I was considering Colin Wilson's discussion of the prevalent pessimism in philosophy - worse in the past 200 years, but always prevalent.
Most philosophy is an act of self-harm, insofar as it devalues life; insofar as it has the view that it would either be better never to have been born, or that life may be pleasant or unpleasant, but ultimately makes no difference to anything...
I have always affirmed Colin Wilson's basic optimism - but in a not-created world and absent a creator who is good and who loves us; I would have to admit that the pessimists are correct!
Because CW avoided metaphysics, his discussion operates at the level of feelings. He argues that our happiest and best, most meaningful feelings are correct about life - yet in the deepest analysis, if these are just feelings, then that basic situation is a pessimistic one.
In contrast is the Nobel prizewinning author Samuel Beckett, whose work is an act of self-harm, directed at harming others - designed to make life pessimistic, to persuade that despair is the rational response to this world. The read Beckett with seriousness is the psychological equivalent of slashing one's own wrists, or drinking poison.
Of course we want to be happy and optimistic (at least, we want this with a part of ourselves) but this happiness must be True. To mean more than just a fleeting emotion, flickering in the mind of a finite being; happiness needs to derive from Good news about Reality. Otherwise the situation would be that Beckett is describing reality correctly; and Wilson's denial of pessimism is merely a way of feeling, and perhaps functioning, better - in what is otherwise an intolerable universe.
So philosophy is only about what we feel unless real-life really-is Good.
For William Arkle his optimism was based on his knowledge (and awareness) of the fact that this is a created reality, and the creator is our loving Father - so reality is designed-around each of us, and what we most need.
Furthermore, Arkle is convinced that we personally chose to be born into our lives. So - with these underpinning convictions - we have an essentially 'optimistic' situation, in which our life is has purpose, meaning, is specifically what we need; and this actual life (its situation) was specifically chosen by our-(pre-mortal)-selves. Therefore William Arkle's philosophy is more than just about feelings.
What 'evidence' does Arkle have? Quite simply: intuitive conviction. Arkle asked basic questions of reality, and knew the answers directly. He asked - is there God, is this reality created - answers came yes. Then, he knew by direct apprehension that this God was Good, and loved him. Looking around at life - he recognised meaning and purpose everywhere and in everything.
Arkle might have been happy merely because he was optimistic by nature - as was Colin Wilson. The two men were indeed good friends, and would have long conversations together, keeping in touch from the 1950s into the 1990s. And on the surface, they were saying similar things.
Implicitly, I suspect that Wilson did have similar beliefs to Arkle - but he was not aware of them, and did not state them explicitly. Therefore, Wilson's work can reduce to self-help - to advice on how to be happier and more optimistic.
But the fact that Arkle stated his fundamental assumptions meant that his happiness and optimism were linked to, and derived-from, ultimate reality by means of stated assumptions. Thus Arkle, unlike most philosophers, broke-through from self-help to metaphysics.