"Their arrows are sharp, all their bows are strung; their horses' hoofs seem like flint, their chariot wheels like a whirlwind. Their roar is like that of a lion, they roar like young lions; they growl as they seize their prey and carry it off with no one to rescue." NIV translation
Isaiah describes how the people that God has chosen as an instrument of his judgement are prepared. Like a lion after it has seized it's prey, there is no rescue for those who have turned their back on God.
"In that day they will roar over it like the roaring of the sea. And if one looks at the land, he will see darkness and distress; even the light will be darkened by the clouds." NIV translation
Isaiah tells of the day that God uses the nations to bring judgement on his people. It also describes the day that Jesus was crucified for our sins as, on that day, it became dark in the middle of the day.
Even as God was bringing judgement on his people as Isaiah described, he already had a plan to reconcile all people to him. That, my friends, is how awesome God is!