God gave Noah warning of impending judgement, so that he could take action. Noah could not prevent or avoid the Flood; but by obeying God’s instructions he could survive it.
That obedience must have cost him a great deal – in time, in expense and in labour. He could not build such a large object as the Ark in secret; so he probably also had to endure the ridicule of his neighbours (who must have thought him mad). But he paid more attention to what God had said than to what they were saying. In the end, his faith was vindicated: when the catastrophe finally struck, he and his family were the only survivors.
Noah’s life illustrates a number of principles. Firstly, faith and action are inseparable: on one level he was saved because of his relationship with God, but also (on another level) because of the boat he had built! Secondly, faith marks us out as different from the rest of the world, both in lifestyle and in destiny. And finally, those who live by faith need not fear the coming judgement; for God will account them as righteous and deliver them.