Karma is the most important integral component of spirituality. In absence of doctrine of karma, spirituality as detailed in Bhagavad Gita can never be understood. It is only when human beings indulged in karma, one evolved from within.
If one was spiritual, the evolution was faster.
As per Bhagavad Gita we are primarily a spirit, a soul atman a cosmic traveler that manifested human body to cleanse self of dross impurities within. Indulging in karma is a necessity for soul atman within. Unless human beings indulged in karma souls atmans could not evolve.
For life to grow in cosmic system, for souls atmans to reach state of absolute purity indulgence in karma by the physical manifest self is an absolute necessity. Karma is the connecting link between two phases of life.
The moment death occurs on mother earth; the released spirit, soul atman immediately manifests a new body to start new cycle of life. The spirit, soul atman remaining the same only the outer covering, the manifest physical body changes!
The residual balance of karma at the time of death becomes opening balance for new manifestation. It is primarily the residual balance of karma at the time of death that decides what form soul atman manifests in next manifestation.
Karma truly facilitates movement of life from one body to another. It also facilitates evolution. Life in cosmic system evolves when the manifest physical body indulges in karma.
Every single moment of life is guided by karma. As our indulgence, accordingly the manifestation! Every single thought precipitates into an act of karma. Even if we are idle karma continues its work in the background. None can stop this action of karma, not even God Almighty.
It is karma that facilitates removal of dross impurities within spirit, the soul atman. Spirituality as detailed in Bhagavad Gita advises human beings to indulge in nishkama karma yoga, offering fruits of karma performed to God Almighty all the time. This way indulgence in karma is not binding. Nishkama karma yoga does not produce a karmic debt, a karmic balance.