A quick response to your carefully worded post:

What can it mean, after all? What can it mean that does not imply an arcana of mystical knowledge? How can one be spiritually ascendent if there is no spiritual world in which to ascend? And I am far from certain that such a world does exist.

I see two issues here. First, as you ask, does a spiritual world exist? I have to admit that I don't really know; in fact, I haven't a clue. Therefore, rather than try to answer a question I think is unanswerable, I try and answer a different question: What is the effect of believing that a spiritual world exists?

In my own case (and this is very personal), I find the effect to be negative. This 'world in all it's multifaceted splendour' as Dant writes above, as I experience it and find it, holds enough for me - no need to postulate a 'spiritual world'.

I also find that in practice, people who choose to believe in a spiritual world are usually (not always, but usually) imprecise, vague, unable to say what they clearly mean, indulge in magical and wishful thinking, non-critical, anti-rational, think they are superior, or at least have superior insights or methods of obtaining knowledge - in short, plain annoying!

Secondly, my discomfort with your 'spiritual ascendency' phrase was not just that if there is no spiritual world (or to be more accurate, I choose to act and think as if there is not) then it makes no sense to be ascending in it. But more it is the sense of superiority, smugness even, that such a phrase engenders in me.

The important question then becomes: if I reject the whole 'spritual' trip, and all the baggage that goes with it, can I rescue anything that leads me to live life to the fullest, realise my potential as a human being, whatever that may be, see and live in harmony with the essential beauty of the world, love myself and others truly - without becoming mushy and sentimentalist about it all? My answer to my own question is Yes.