the message means that if we are good and do things for the good of others and the society, nature gives us good things to enjoy and we can have a happy and satisfactory life. Just like the Abbot. he was a kind hearted man and tied the Inchcape bell to the inchcape rock so that the sailors would be warned of the inchcape rock and their lives would be saved.
On the other hand, if we are bad, and our actions are for the loss of others and the society, nature gives us bad things and we would suffer and repent for our mistakes. This holds good for the pirate. he was cruel and jealous of the abbot. He cuts the inchcape bell off the buoy , causing danger and a lot of shipwrecks in that area. However, in the end, bad luck finds him and he repents for his own mistake. He finds his fate.
This is the law of nature. This poem is suitable for this message.