In the context of the play, this passage means that Macbeth is already prepared to give up on life after the death of his wife and is contemplating life and the universe. In addition to showing Macbeth’s unhappiness, it could be meant to signify the end of Macbeth’s reign of terror on Scotland, the end of his will to live, and the end of his life. The passage reflects on humanity as a whole because the lack of grief expressed by Macbeth at the announcement of his wife’s death and the contemplation he does following the announcement seem as though they were written specifically to cause the reader(s) to ruminate if anything humanity does really matters in the grand scheme of things while feeling sympathy for Macbeth due to his situation.
