Use it and lose it

Yes, we know it's true. While we live and still have the power, we preserve our ability to do by doing—to think by thinking, to dance by dancing, to love by loving. We use it or lose it. Nevetheless, as Philip Larkin (1922-1985) reminded us in his poem "Dockery and Son":

Life....
Whether or not we use it, it goes,
And leaves what something hidden from us chose,
And age, and then the only end of age.

– from The Whitsun Weddings, 1964

I wonder, though, at that choosing by "something hidden from us"; what might Larkin have been referring to? Was he a closet pantheist, god immanent in the natural cycle of life and death? Or was he simply saying that, be born and die as we must, we do not know why and cannot ultimately choose, any more than those primitives depicted in Paul Gaugin's fine painting, "Where Do We Come From? What Are We? Where Are We Going?"