"Sustainable" in a poem

As I have mentioned previously, April is National Poetry Month and also Mathematics Awareness Month -- and the mathematical focus is "Mathematics of Sustainability."  To try to connect these April celebrations, I went to the website  www.Poets.org  and searched for a poem containing the word "sustainability."  There I found  "Patience" by Kay Ryan which contains these lines:

       Who would
       have guessed
       it possible
       that waiting
       is sustainable —
       a place with
       its own harvests.    

Please go here to Poets.org to read Ryan's entire poem.
Also at www.Poets.org I found "Looking" by Robert Kelly, containing the word "sustain"; here are a few lines from Kelly's poem; for the entire poem go here (at Poets.org).

     . . . I wanted a universe
     that sustains
     looker and looking and the seen
     forever, detail after detail
     never ending. And all I had found
     was between.

What does "forever" mean?