That Christ Both Is and Was ImpeccableFor God to sin would be a contradiction, for it would be for him to declare, by his actions, something true which is not. If God says that a thing is true, then he does so out of his character. God created what is because of his character, and thus what God says and what God has said is true are both due to the same thing: God's character.
Christ lost none of the essential attributes of God when he was born as a man. If he had lost an essential attribute of God, then he would no longer be God, but Christ is God. If he were not God, then he would not have had the ability to bear the degree and amount of suffering which is due to us on account of our sin.