Thus says Yahweh of Armies, 'I have marked that which Amalek did to Israel, how he set himself against him in the way, when he came up out of Egypt.

Now go and strike Amalek, and utterly destroy all that they have, and don't spare them; but kill both man and woman, infant and nursing baby, ox and sheep, camel and donkey.'"

Saul came to the city of Amalek, and laid wait in the valley.

Saul said to Samuel, "But I have obeyed the voice of Yahweh, and have gone the way which Yahweh sent me, and have brought Agag the king of Amalek, and have utterly destroyed the Amalekites.

Because you didn't obey the voice of Yahweh, and didn't execute his fierce wrath on Amalek, therefore Yahweh has done this thing to you this day.