This is a very good question. The combination of metaphor and simile in the lines you refer to are most difficult to understand. What Macbeth seems to mean is that everybody in Scotland, and perhaps also in England, will feel pity for the murdered Duncan. This will cause many people to shed tears and it would be the figurative tears that would be blown into every eye. The entire metaphor-simile concludes with "...that tears shall drown the wind." The wind will blow the tears all over the kingdom, but there will be so many tears that they will stop the wind from blowing. The revelation never actually happens. I don't think pity spreads the news but only spreads the pity, which would work to Macbeth's disadvantage if and when he becomes king because it would be natural for people to suspect the person who benefited from Duncan's death. Both the naked newborn babe and nature's cherubin are supernatural creatures, so they would possess supernatural powers to influence the entire population. Macbeth seems to be victimized by the supernatural throughout the entire play.