Swami Mukundananda
Why can't I ever finish working off my past karma?
The stockpile of karma never ends
We carry a stockpile of past karmas, called sanchit karmas, and God's system of justice is that we bear the consequence of whatever we did. Since the stockpile is infinite and we keep adding to it, there is one recourse: the law of grace.
Since we have had infinite lives, our stockpile of karmas is infinite. To burn them all would take infinite lives, and while burning them we keep doing more karmas.