The cross represents the foolishness of man and the power of God. Men crucified the Lord Jesus and then called for Him to come down from the cross. It was the will of God for His Son to die on the cross and make atonement for our sins. God s providence is working. The sea is not to be governed by man.
Ships move across the sea like a sheet of paper blowing in the wind.
Ships move easily across the waves of the sea. The sea cannot be restrained, chained nor kept in check nor managed by man. So it is with the providence of God. Napoleon was a man of war. He was victorious over nations, but he could not conquer the ocean.