Nonno's poem is significant on several levels. First, the elderly poet has finally completed a new work. He dies, apparently content after doing so.
Second, Nonno has few lines in the play and largely functions as Hannah's charge. Caring for her grandfather as they travel gives her life some purpose. In another sense, however, he holds her back. Nonno seems to hear what the others say, so he is somewhat aware of Hannah's and Shannon's conversations.
In the latter regard, the poem's content is also significant. It is about observing in contrast to doing, hope versus despair, and about second chances. Everyone in the play is at the end of their rope in some regard. Shannon is a wreck of a man, Hannah has few options, and Nonno is at the end of his life. The poem's meaning largely parallels that of the play. Nonno is Hannah's rope, and his death frees her. Shannon is his own worst enemy, who needs a new lease on life; he literally gets tied up. While Hannah' compassion saves him, he in turns shows compassion to the iguana, which represents his second chance- the "second place to dwell... in the frightened heart."