«اسْتَغْفِرُوا رَبَّكُمْ إِنَّهُ كَانَ غَفَّارًا»
“Ask your Lord for forgiveness; indeed, He is ever most forgiving.”
Istaghfirū and ghaffārā share the root associated with forgiveness. The earlier imperative calls for pardon, and the later description explains why such a request is fitting.
The verbal echo also supplies reasoning: the act of seeking forgiveness is connected to the divine quality of granting it. Meaning leads; sound reinforces it.