Our speaker of "When Lilacs Last in the Dooryard Bloom'd" sounds like Whitman's go-to universalized "I" first-person voice. By "universalized," we mean that, although the speaker uses the word "I," he does so in a way that extends the meaning of that "I" to all of us. We're all part of the speaker's perspective. (Now don't you feel special?) And since he's talking about life, death, grieving, and celebration, we can—and should—all relate on some level.
So, in a way he's like some super first-person speaker who often speaks from an omniscient point of view as he sweeps the nation's landscapes. First, we're in a dooryard, then we're in a mysterious swamp, then we're attending funeral processions, and then we're hanging out with death, a hermit-bird, and a western star. It's like a whirlwind: "over the breast of spring, the land, amid cities" (26). Through it all, the speaker sounds like an everyday (though still poetic) kind of guy who's being honest about his feelings and isn't afraid of letting loose with one "O!" after another.
And because the speaker covers so much ground in a rather thorough fashion, we really sense his grasp on the nation as a whole. It's okay if he's a little long-winded because, well, he kinda has to be in order to truly bring "blossoms and branches green to coffins all." We know from the beginning that he's extending his elegy to all who grieve, so we kind of have to cut him some slack for being all over the map at once.
The speaker also tends to take us for an emotional rollercoaster ride when it comes to his "ever-altering song," and he admits to being all over the map in the final section of the poem. But hey, that's how grieving goes. If the elegy sounded too smooth and controlled, we wouldn't really feel the speaker's honesty. One minute we're grieving, the next we're joyful, and by the end we're feeling all things at once, if in a somewhat peaceful way. And we have the speaker to thank for that. After all, he's the one who's brought us through so many different emotions and landscapes. He's like the most intense tour guide ever.