This poem leaves a lot up to the imagination. While we know that Octavio Paz wrote the poem, we don't have to confine our imaginations to think of Paz as the speaker. In fact, one of the quickest ways to get into trouble when reading poetry is to confuse the speaker with the writer. They're often not the same.
So, what do we know about this speaker? He could be a young man, passing by a cemetery on a long walk, watching a family mourn an old woman. Or he could be an old man, confined to a wheelchair, watching the lowering of a family member into the tomb. Perhaps the dust of his own wife awaits him, or perhaps he is close to becoming dust himself.
In the poem itself, there are some hints about what kind of person the speaker is, regardless of his motive for writing the poem or his relationship to this woman. There is no first person pronoun (I) in the poem, so we have to deduce everything we know about the speaker through careful reading.
First, the speaker seems somewhat distant from the woman he is describing. The poem is an epitaph for an "Old Woman," not "my mother," or grandmother. Possibly, this could mean that he (and we're just assuming it's a he) is just the kind of person to be deeply moved by the drama of life and death, whether or not it's the life or death of someone close to him. Yet, since this is an epitaph, it is supposed to be short, so maybe he does know this woman quite well, but is sparing details for the sake of space. In any case, the speaker demonstrates a pretty matter-of-fact attitude toward the woman herself.
Of course, we only get six lines from his perspective. Since he thinks about the woman's husband in the tomb, we can guess that he's sensitive to the enduring power of love. When he thinks about this old woman being buried, his thoughts are moved to beyond the physically possible. He's not afraid to picture the dust of this woman's husband trembling as it anticipates her arrival. Even in the face of death, our speaker envisions romance and love. In this way, we can view him as sympathetic to the influence of romantic love.
Yet this joy, he seems to think, is the reason for sorrow upon death. He sees both sides of the coin. In that way, he's both a magical-thinking romantic, and a mournful realist. He doesn't really come down on one side or the other. Perhaps he's unwilling to take a stand himself, or perhaps (more likely) he's inviting our own thoughts on the matter. Rather dispassionately, he presents both cases for viewing the afterlife, and then leaves it up to us to decide how we'd like to view this scenario. What a swell guy!