# So why have you despised ... Yahweh, so as to do what is evil in his sight?

"You should not have despised ... Yahweh and should not have done what is evil in his sight!" 

# what is evil in his sight

"what he considers to be evil" or "what is evil in Yahweh's judgement" 

# You have struck down Uriah the Hittite with the sword

"You have arranged for Uriah the Hittite to die in battle"

# You killed him with the sword of the army of Ammon

"You arranged for him to die in battle against the army of Ammon"