وَأَمَّا بِنِعْمَةِ رَبِّكَ فَحَدِّثْ
And speak of the blessing of your Lord.
The third ammā clause maintains the parallel form but changes from a negative prohibition to the positive imperative fa-ḥaddith. The previous two directives concern conduct toward others; the closing directive concerns acknowledging divine favor.
The closing combines structural parallelism with a meaningful shift of command type, ending in a positive act of gratitude.