Hi there!
The advice the poet would give to the grieving Margaret in “Spring and Fall” is that is important to understand death as a normal cycle because everything and everybody has a limited time in this life.
As you grow older, you will see many tragic events happen, but that is just a part of life. Even though death is a natural process of life, it’s important to know that everyone dies and everyone lives and their death should be a celebration of their life not to mourn their passing.
Hope this helps!