«جَنًى ... جَنَى غَرْسِهِ»
Fruit ... the fruit of his planting.
The poem repeats janā, first as the result someone asks for, then in connection with what that person planted. The sound ties together a claim and its source: one cannot separate the desired harvest from the earlier cultivation.
«كُلُّ مَنْ ... فَمَا لَهُ إِلَّا ...»
Whoever ... then nothing is his except ... .
The construction mā ... illā creates restriction or exclusivity. It places the outcome, according to the poet's declared policy, in relation to the person's own conduct.