This tells the reader to pay special attention to what follows. Alternate translation: "Look" or "Listen" or "Pay attention to what I am about to tell you"
Here Yahweh's power is represented by his "hand." Alternate translation: "I will turn my powerful hand against the Philistines" or "I will turn my great power against the Philistines" (See: [[rc://en/ta/man/translate/figs-metonymy]])