Karmic debt is created when an atman starts its cosmic journey. All atmans before the start of their cosmic journey are pure. No sooner Brahman, God Almighty exploded self with a big bang, all pure atmans scattered all over cosmos at unimaginable speeds.
In the melee, pure atmans get mired in impurities and to cleanse self of dross impurities within it needs manifesting a body to work out its karma.
In absence of karma, evolution no atman could purify itself, regain its lost original pure prime pristine primordial form.
Karma is that inherent principle of cosmic life that facilitates movement of life from one manifestation to another. In absence of karma and evolution the whole world of atmans would go haywire, remain inert forever.
Of their own no atman could purify itself and needs a body, a medium to cleanse itself.
When an atman manifests human form for the first time, it gets an assurance that if the incumbent human being indulged in spirituality detailed in Bhagavad Gita, it could reach state of absolute purity forever. And thus start promptings of atman from within our heart.
From six years of age I have been distinctly hearing voice of atman come from within my heart. Dominated by ego most human beings world over did not hear voice of atman come from within. If we can demolish our ego (not suppress) by indulging in spirituality detailed in Bhagavad Gita and also become 100% truthful in life, we can clearly hear voice of atman come from within our heart.
Indulging in karma is a cosmic requirement of atman and human beings could do nothing about it. We all have to indulge in karma no matter what. Karma cannot be equated to physical work alone. As per Jainism doctrines every single thought precipitates into an act of karma.