Derek Walcott's poem "Veranda," is about death and transition; it's about the links between the past and present. In the first part of the poem, the speaker remembers a time when the West Indies was a colony of the British Empire. In the second part of the poem, the speaker invokes the spirit of his dead grandfather, and in the third part of the poem, the speaker reflects upon and anticipates his own death.
In the first part of the poem, the speaker describes the colonial past of the West Indies as "a fading world," populated by "Grey apparitions" of "Planters," "Colonels," "middlemen, (and) usurers." It is a world now reduced to "smoke" and "ashes" but which still has the power to haunt the present. The implication here is perhaps that the past never really dies and always lives on, in some form or other, into the present.
In the second part of the poem, the speaker describes the ghost of his grandfather who "sought (his) Roman / End in suicide by fire." Explaining why he has invoked his grandfather's spirit, he says that it is because his grandfather's "house has voices" and because his grandfather's
genealogical roof tree, fallen, survives,
like seasoned timber through green, little lives.
In other words, the speaker has invoked his grandfather's spirit because his grandfather has left behind him a legacy which runs throughout the speaker's life. The overall idea here is the same as that expressed in the first part of the poem—the past never really dies and is always inseparably, inextricably linked to the present.
In the third part of the poem, the speaker reflects upon his own impending, inevitable death and anticipates his transition from the corporeal world to the "vaporous world" of "smoke" and "ashes." He says that he "ripen(s) towards ... twilight ... that dream ... (or) sea-crossing." The word "ripens" is interesting here because it suggests that this transition, from life to death, is not an end but rather a beginning, for which life has been only a preparation. At the end of the poem, the speaker says that he reaches out with "a darkening hand to greet those friends," including his grandfather, from the "vaporous world." The suggestion here is that life is a transition towards the spiritual, ethereal world of the dead.