The poem begins with the speaker declaring that he has a "rendezvous" with death. A "rendezvous" is a meeting or appointment, and this line thus suggests that the speaker's encounter with death has already been planned out or decided upon, that the speaker's death has been somehow predetermined. Of course, this is impossible, but this idea underscores the extent to which the speaker is sure that he will soon die. The word "rendezvous" also has certain military connotations, since it is often used to refer to an assembly point where troops are supposed to meet or gather.
The militaristic association that comes along with the word "rendezvous" helps make sense of the phrase "disputed barricade" in line 2, clarifying that the speaker is alluding to the front lines of a battlefield, where the "disputed barricade" is the clash of two armies fighting to gain new ground. This, in turn, implies that the speaker expects to die in combat.
At the same time, the idea of meeting death at "some disputed barricade" could also be interpreted as an acknowledgment of the uncertainty surrounding the actual experience of death. After all, even if the speaker is confident that he'll die on the battlefield, he has no idea what it will be like to actually pass through the barrier between life and death. It is this sense of uncertainty, then, that makes the "barricade" between the world of the living and the world of the dead feel "disputed."
Furthermore, lines 3 and 4 associate the speaker's upcoming death with the emergence of spring. Consequently, a sense of juxtaposition arises between the imminent end of the speaker's life and the kind of rebirth and continuation that spring represents. Accordingly, it becomes clear that the speaker recognizes that the world will go on without him, continuing to blossom in beautiful ways despite the fact that he's destined to die a bloody death on the battlefield (at least according to him).
Though one might expect this to upset the speaker, he seems relatively unfazed by the idea of his own death. Rather than bemoaning his unfortunate circumstances, he simply states—without any apparent display of emotion—that he will soon meet death, and his lack of sentimentality regarding this idea suggests that he has accepted this as his fate.
It's also noteworthy that these opening lines establish the overall rhythm of the poem. The speaker uses iambic tetrameter, meaning that each line contains four iambs: metrical feet consisting of an unstressed syllable followed by a stressed syllable. This creates a da-DUM da-DUM rhythm that runs throughout the poem:
I have | a ren- | dezvous | with Death
In addition, readers will notice that the second and third lines include end rhymes ("barricade" and "shade") but that the first and fourth lines do not; interestingly enough, this is not the beginning of a set rhyme scheme, but rather an example of how the speaker employs random rhymes, matching certain lines with each other to enhance the sound and musicality of the poem without committing to an actual pattern.