Not waving but drowning

Nobody heard him, the dead man,
But still he lay moaning:
I was much further out than you thought
And not waving but drowning.

Poor chap, he always loved larking
And now he’s dead
It must have been too cold for him his heart gave way,
They said.

Oh, no no no, it was too cold always
(Still the dead one lay moaning)
I was much too far out all my life
And not waving but drowning.

A hauntingly simple short poem by Stevie Smith, whom I admire greatly. I find the last two lines suddenly overcome me; please tell me what you make of it. I first came across her work casually browsing in the library. Therefore libraries are good.