The meaning of the poem "The Shapes of Death" by Stephen Spender is that knowledge of our mortality is something that hangs over our lives and often influences our thoughts and behaviors, contributing to our fears and anxiety. This is brought out in the first line of the poem:

Shapes of death haunt life,
Neurosis eclipsing each in special shadow:

Stephen Spender, in this poem, indicates that we strive in life to achieve many things.

Ambition is my death. That flat thin flame
I feed, that plants my shadow.

However, in the end, the underlying feeling in this poem is that we all will die and it seems that the poet is alluding to the fact that there has to be more to life than all this striving. The poet even indicates that unbridled ambition can be a stumbling block to finding and engaging in true love. The poet is saying that unrelenting, driving ambition can set us on a course whereby we don't take time to enjoy and appreciate other things that are really important in life.

The last stanza of the poem conveys the message that we can find beauty and comfort in the natural world around us. The swallows that the poet sees will not save him from dying one day, but they are a comfort to him as he struggles in his earthly existence. Something as simple and beautiful as watching swallows are comforting to him against the backdrop of the bigger issues of life - Love, Death, Achievements, and more.