The old man thus confirms the evil that has occurred, and his testimony is all the more significant as he is older and has seen more. Basically, the bewilderment that this night has caused for him shows the intensity of the night's evil: " "T is unnatural,/ Even like the deed that's done" (II.iv.10-11). It is a known truth that what is unnatural is most often considered evil, as it is different, not normal. In fact, even Macbeth himself agrees that " "T was a rough night" (II.iii.57). So if the weather even worries the murderer himself, it must mean that it was truly an illustration of the evilness of the deed. The fact that such a great warrior, and killer of men, is so lost in terrifying guilt indicates the full extent of the evil he has committed. Nature thus foreshadows or exhibits a particular evil that will or has happened on the night of the event.
Similarly, there is, during the whole of the play, an opposition between light and dark which is paralleled to that of life and death, as well as good and evil. It is important to acknowledge the fact that both Duncan's and Banquo's murder takes place in the dark. The latter notices, on the night of the king's death, that the stars are not shining, meaning that the murder does occur in complete darkness: "There's husbandry in heaven;/ Their candles are all out" (II.i.4-5). The fact that the lights are out in heaven signifies that there is no longer any appearance of good, thus foreshadowing the evil that will strike. The night of Duncan's assassination is further compared to Christ's crucifixion and the great darkness that enveloped the land by Rosse when discussing it with the old man: Thou seest, the heavens, as troubled with man's act,/ Threatens his bloody stage: by the clock "t is day,/ And yet dark night strangles the travelling lamp. [.] That darkness does the face of earth entomb" (II.iv.5-8). The unnatural state of things is thus paralleled to the darkness that has usurped the place of light.