The diction Yeats uses in this poem is definitely elevated and reminiscent of courtly, literary, and religious speech. He uses series of three to give a sense of authority and all-encompassing completion in these phrases: "fish, flesh, or fowl," "begotten, born, and dies," and "past, or passing, or to come." Religious sentiment comes through in the phrases "holy city," "God's holy fire," "mortal dress," and "artifice of eternity." A literary or courtly mood is evoked by such words as "monuments of unageing intellect," "studying monuments of its own magnificence," and "to lords and ladies of Byzantium."
Yeats uses powerful metaphors to express the speaker's feelings about growing old and dying. He compares "an aged man" to a scarecrow: "a tattered coat upon a stick." The speaker's exploration via his imagination of how he wants his end to come is compared to sailing the seas. He wants ancient sages to be "the singing-masters of my soul"; in other words, he wants these purveyors of ancient wisdom to show his soul how to pass from this life into the next. He likens his own aging body to "a dying animal."
The pervading symbol of the poem is Byzantium, which represents Yeats' idealized afterlife. The historic city of Byzantium, or Istanbul, fascinated Yeats because of its great artistic splendors, and he once stated that if he could go back anywhere in time for a month, he would go to Byzantium in the 6th century. Thus the speaker's preferred locale upon leaving this life—incorporating "what is past, or passing, and to come"—is to be reincarnated as a golden statue of a bird that would sing to the Emperor and lords and ladies of that romanticized setting. As a poet, Yeats' talent and joy is conveying his thoughts through lyrical verse, and the singing of the golden bird represents a continuation of that joy for eternity. Having an audience of an Emperor and lords and ladies represents any writer's desire to have worthy and notable recipients on whom to pour out his or her ideas.
Yeats uses elevated diction, rich metaphors, and elaborate interwoven symbols to convey his sentiments about passing from this life into the next.