Yeats, grappling with his own advancing years, explores the inevitability of death and the challenges associated with old age. The poem presents a bitter contrast between the vitality of youth and the decline of old age, emphasizing the temporary nature of human life.

The speaker laments the physical limitations of aging, describing themselves as "A tattered coat upon a stick," much like a scarecrow. This imagery vividly conveys the decrepitude and vulnerability accompanying old age. The speaker wants to escape these limitations and achieve a more permanent form of existence.

Yeats also explores the psychological challenges of aging, such as the fear of death and the loss of vitality. In the poem, he writes, 

Consume my heart away; sick with desire
And fastened to a dying animal
It knows not what it is.

The speaker holds a deep-seated anxiety about their inevitable death and longs for something more than their earthly existence. By confronting these universal human anxieties head-on, Yeats uses the poetic form to explore the complexities of aging and death in a way that is both thought-provoking and emotionally resonant.

In "Sailing to Byzantium," Yeats suggests that art can serve as a means of transcending the limitations of mortality and achieving a form of immortality. By creating works of art, a person can leave a lasting legacy and become a part of the cultural heritage of humanity.

In the poem, the speaker yearns to become a "singing-master of my soul," suggesting that art can serve as a spiritual guide and source of transformation. The imagery of the golden statue and the mosaic, both products of human artistry, symbolizes the speaker's desire to become something eternal and beautiful.

Yeats also emphasizes the power of art to preserve and transmit knowledge and experience across generations. The speaker imagines singing to the lords and ladies of Byzantium, "Of what is past, or passing, or to come." Yeats believes that art can serve as a means of connecting the past, present, and future. If he can join the "sages standing in God's holy fire," he too can influence future generations long after his death.

Yeats presents a stark contrast between the natural world, characterized by growth, decay, and mortality, and the artificial world of human creation, which can offer a more lasting form of existence.

The speaker yearns to escape the limitations of the natural world, which they associate with aging and death. They see their physical body as a product of nature and subject to its laws. They long to be transformed into something more eternal that can be preserved as a work of art.

However, the poem also acknowledges the beauty and vitality of the natural world. The speaker admires the "salmon-falls, the mackerel-crowded seas," and the "birds in the trees." These images show that nature can be a source of wonder and inspiration, even as it is subject to the cycle of life and death.

Ultimately, the poem suggests that humanity's relationship with nature is complex. It is characterized by both admiration and alienation. While nature can be a source of beauty and inspiration, it can also be a source of limitation and mortality. Humanity can move beyond these limitations by creating works of art and culture. This idea reflects the modernist worldview, which often celebrated human achievements and technological progress as a means of overcoming the restrictions of the natural world.