This is the 13788th most frequent German word.
ergreift
"Ergreift" means "grabs," "seizes," or "takes hold of."
The verb "ergreift" here is used in the sense of taking or seizing an opportunity.
Ergreift die Gelegenheit, wenn sie sich euch bietet.
Seize the opportunity when it presents itself to you.
In this context, "ergreift" conveys an emotional impact, effectively "gripping" the listeners.
Die Rede ergreift die Zuhörer und bewegt sie zutiefst.
The speech touches the listeners deeply and moves them profoundly.
Here, "ergreift" is used to mean physically seizing or catching the thief.