'Spiritual need' reminds me of what C S Lewis wrote about Sehnsucht - a German word for yearning or longing. He said there can be an inconsolable longing in the human heart for we know not what, 'a desire for our own far off country ... for something that has never actually appeared in our experience'.
He wrote of experiencing this piercing desire 'at the smell of a bonfire, the sound of wild ducks flying overhead, the title of The Well at the World’s End, the opening lines of Kubla Khan, the morning cobwebs in late summer, or the noise of falling waves.' I think different things provoke it in different people.
This was a factor in Lewis's conversion to Christianity. The Bible says, 'He has put eternity into the hearts of men.' (Ecclesiastes 3.11)
Lewis wrote:
'Creatures are not born with desires unless satisfaction for those desires exists. A baby feels hunger: well, there is such a thing as food. A duckling wants to swim: well, there is such a thing as water. Men feel sexual desire: well, there is such a thing as sex. If I find in myself a desire which no experience in this world can satisfy, the most probable explanation is that I was made for another world.'
(C S Lewis, Mere Christianity, my emphasis)
This may not be quite what Caleo is thinking of, though.