Question

Why does the speaker in "Spring and Fall" tell Margaret that the source of her sorrow is "the blight man was born for"?

Answer 1

Here is a website that will help you find the answer and understand the poem as well...
http://www.sparknotes.com/poetry/hopkins/section4.rhtml

If you do not wish to visit the site I believe the answer is A.
Because she is mourning her own mortality, because man is mortal.

Answer 2

The answer is A. He is suggesting that, even though she cannot yet express it, Margaret intuitively recognizes the mortality of all human beings.

I took the test. Hope that explained