Moore's Eternity

Marianne Moore's "What Are Years?" is a pretty profound dialogue on growing older, death, and eternity. There were two passages that really made me think about the concept and kind of gave me solace.
The first is "He / sees the deep and is glad, who accedes to mortality / and in his imprisonment rises / upon himself." The meaning I got from this was that the bird (the supposed subject of the poem) was able to look upon eternity (the deep) and was glad that he was not forced to exist in it, that his existence was temporary. I can sympathize with this because I feel that having to exist forever would be very wearying and mentally overwhelming. Having a temporary existence, in a way, is motivation to make the best of life. If you live forever, there's always tomorrow.
The second passage reads: "Though he is captive, / his mighty singing / says, satisfaction is a lowly / thing, how pure a thing joy is." This correlates with the second half of the previous quote, but focuses more on the fulfillment and enjoyment of striving to extend your mortal impression as far as you can. In many ways this reminds me of "Ode to a Nightingale" where the speaker speaks admiringly and enviously of nature's immortality. He/she realizes, however, that the temporary quality--the mortality--of life is what makes it so invigorating and special. Having no end or beginning takes the momentary enthrallment out of life. In this way, the speaker of "Ode" realizes that his/her current peace and happiness is the apex of life and is finally willing to pass on.
The bird, and therefore the speaker, of "What Are Years?" is reaching the same conclusion: he/she is grateful for the passion of life that mortality brings, and ultimately prefers it over the vastness of eternity. The final lines, "This is mortality, / this is eternity" sums up the revelation: live for the moment and you can experience eternity in everyday life.