Definition of spirituality is one from times immemorial, ever since mother earth came into being.
The word spirituality stems from spirit, the underlying abstract reality existing in all living beings. The consciousness existing in our heart is called soul atman in Hinduism.
When human beings took an inner journey towards this spirit, consciousness the path is termed spirituality. The inner journey towards consciousness, soul atman is necessitated as primarily we are a spiritual being, a cosmic traveler manifesting human form.
As a spirit we manifest human form to work out our karma, remove dross impurities within. Ever since this spirit, soul atman separated from its source Brahman (God Almighty) it desires regaining its lost original pure prime pristine primordial form at the earliest.
This becomes possible when human beings indulging in spirituality finally succeed reaching state of enlightenment in their lifetime. Enlightenment announces a soul atman, the spirit gaining absolute purity forever. In absence of dross impurities within this spirit need not manifest a human body again. The need to manifest human form now ceases to exist.
Definition of spirituality is best detailed in Bhagavad Gita, the sermon given by Lord Krishna to Arjuna in the battle of Mahabharata. Every human being on mother earth must bear one thing in mind; in absence of teachings of Bhagavad Gita none in this world could gain enlightenment.
It is Bhagavad Gita that clearly defines what spirituality was all about and how to cover this inherent journey.
As per Bhagavad Gita spirituality demands demolition of ego in totality! To establish total control over five senses and mind human beings need reducing their desires and wishes in stages.
Every moment thousands of thoughts passed through our brain. Even as a child we had many queries within… who I am, what is the purpose of human life, our relationship with lower forms of life. Relationship with God, relationship with soul atman and whatnot!
Spirituality was all about dissolving all queries within. Indulgence in jnana yoga gets necessitated so that human beings can demolish darkness of ignorance within forever. To scuttle, negate karma to zero, jnana wisdom contained in Bhagavad Gita is necessitated.
Moment queries within human beings reduced to zero one immediately reaches state of Nirvikalpa Samadhi (state of absolute nothingness) when not a single thought entered our brain uninvoked. This is the state sought by spiritual travelers.
Furthermore practicing absolute celibacy for a period of 12 years in continuation human beings awakened their kundalini energy fully. This results in opening of Sahasra Pushpa (thousand petalled Lotus) existing in brain behind forehead. One immediately becomes an enlightened one, a bodhi, a Jina… a Mahavira forever.
Understanding definition of spirituality followed by path of spirituality detailed in Bhagavad Gita, any human being world over belonging to any religion faith or belief can indulge in teachings of Lord Krishna in Bhagavad Gita to reach stage of enlightenment.
The foremost of all, everything in scriptures including Bhagavad Gita becomes clear only by indulgence in contemplation (chintan), never otherwise. The queries within dissolved only when we contemplated (indulged in chintan), never otherwise!