إِذْ تَمَنَّوْنَهُمْ غُرُورًا فَسَاقَتْهُمْ إِلَيْكُمْ أُمْنِيَّةٌ أَشْرَاءُ
Meaning: When you recklessly wished them to come, the arrogant desire you entertained became the means of bringing them toward you.
Ghurūran expresses self-deception or overconfidence; umniyyah is a wish, and ashrāʾ adds the sense of insolent excess, not the price of merchandise.
In fa-sāqathum ... umniyyatun, a wish is made to act as if it could drive an army forward. This is personification: an inward desire is given the agency of physical movement.