One cannot but be what one is; one can only see what one is. Even the word "God" is seen and experienced based on where one is in the continuum of consciousness~being structures.
A conventional person cannot consistently see as a post-conventional person sees. You can argue all day and night for cosmic Love with a group love person, and the arguing will not give the person cosmic-centric eyesight.
Only Spirit, Who is All-Inclusive Love, the Teleological Principle of all emergence, gives this, through the Omega Pull toward Fullness, or the Omega Point. This is embodied as Christ. And, only spiritual Practice (acesis) avails to transform one to cooperate with Spirit in emerging post-conventional processes.
To see cosmically, one must engage life as spiritual Practice to nurture and evolve that seeing, the same way other skills are learned through practice. As you evolve this seeing, or progressively-integrated experience, you integrate less-full seeing into more-full seeing. Nothing is lost; all is taken into the wider Embrace of Spirit.
Wholeness is the Embrace of God, which Grace is drawing us to. This Embrace many Christians call perfection. I prefer to use Wholeness, partly to avoid moralistic-pietistic associations with perfection and sounding literalist-fundamentalist.
So, now to the specific theories of the meaning of being spiritual.
1) Spirituality is attaining the highest levels of any developmental potential. Spirituality is that stable structure of maturity cognitively, effectively, emotionally, morally, …
2) Spirituality is the sum total of the highest levels of developmental potential. How spiritual one is means the equivalence to the potential-realization of all his or her capacities. A person might be evolved religiously and, yet, not evolved socially. The mature person spiritually would have evolved in all capacities to a post-conventional structure.
3) Spirituality is a separate developmental potential, alongside other developmental potentials. Spirituality has it own line of sequential~emergent evolvement. One, theoretically, could be post-conventional spiritually and either pre- or conventional in another developmental potential. For example, a person could be post-conventional morally, while conventional spiritually. A post-conventional, world-centric person spiritually might effectively be pre and conventional, likewise.
This can explain why some persons can grow up spiritually and still be emotionally immature. But, a problem here involves the question, “What is entailed in the spiritual line of development, so that it exists separate?” Once we take away the other developmental aspects, like morality and affect and cognition …, what are we left with that could be spiritual by itself?