Show an affirming flame
This line of the poem is interesting because the poem, in the first stanza, we see the emotions and the feeling of uncertainty, it sets a tone of fear and negativity. The next couple of stanza is more how leaders failed, like in the third stanza, and how we must suffer again. Throughout the poem, do we not only see the bickering between authorities and negative results of it but almost like why fight for life. So this line and this stanza kind of gives a sense of hope that is not present throughout the poem. With these words of "Show an affirming flame," like if Auden wants to start a fire to whoever is listening to him and send a message like yeah, life is good enough to fight too.