What is the meaning of the counsel to a repentant person who has committed grave sins to strive diligently in acts of worship, and how can they reconcile this with work and earning a livelihood?

The meaning of theائب's (repentant one's) exhortation to strive in acts of worship is that he should exert his utmost effort in drawing closer to Allah Almighty and increase his avenues for earning good deeds, because good deeds erase bad deeds. So, he should maintain the obligatory acts and increase in supererogatory acts as much as he can. Work and seeking to earn a living do not contradict striving in acts of worship; rather, work itself is an act of worship for which Allah's reward is hoped, if the intention is pure. Furthermore, this earning should not distract him from any obligation nor lead him into anything forbidden. He should perform supererogatory acts as much as is feasible according to his capacity, while increasing in seeking forgiveness, remembering Allah Almighty, supplicating to Him, and seeking His refuge so that He may accept his repentance and overlook his slip.