The speaker of "since feeling is first" uses alliteration sparingly throughout the poem, quickly moving from one alliterative sound to the next. This adds a subtle sense of melody and cohesiveness to the poem without making it sound overly poetic or constructed. Alliteration helps the speaker create a unified sound, one that draws readers through the poem and smooths out the somewhat haphazard way that the stanzas are organized.
The first line features clear alliteration with the /f/ sounds of "feeling is first," immediately drawing readers' attention to this important phrase that outlines the overall message of the poem—namely, that emotions are the most immediate and therefore meaningful types of human experience. By repeating the /f/ sound, the speaker connects the words "feeling" and "first" to highlight this idea.
Later, the speaker repeats the /l/ sound before switching to the /p/ sound in the last three lines of the poem:
laugh, leaning back in my arms
for life's not a paragraph
And death i think is no parenthesis
The repetition of the /l/ sound links the words "laugh," "leaning," and "life"—all words that carry importance in the poem, as the speaker tries to convince the lover to enjoy life on an emotional, experiential level before it's too late. In other words, the speaker believes that people should laugh and embrace their loved ones while they still can, since life is finite.
To that end, the alliteration of the /p/ sound in the final two lines calls attention to the words "paragraph" and "parenthesis," reminding readers of the poem's extended metaphor that compares life to writing and syntax. In this way, the speaker's use of alliteration helps spotlight an important idea in the poem, which is that life actually isn't a "paragraph," nor is death a "parenthesis." The speaker argues existence shouldn't be approached like a piece of writing, even if the speaker, somewhat ironically, expresses and underscores this idea by using clever syntax and literary devices like alliteration.