فَلَوْ شَاءَ رَبِّي كُنْتُ قَيْسَ بْنَ خَالِدٍ / وَلَوْ شَاءَ رَبِّي كُنْتُ عَمْرَو بْنَ مَرْثَدِ
Had my Lord willed, I could have been Qays ibn Khālid; had He willed, I could have been ʿAmr ibn Marthad.
The repetition of law shāʾa rabbī emphasizes that birth and ancestry are not achievements of personal will. The poet names two distinguished men and imagines an alternative position in society.
This is not a literal claim that his lineage changed. It is a counterfactual comparison preparing for the imagined wealth and descendants in the next line.