"The Question" begins with the speaker declaring that what follows happened in a dream. That is, the journey the speaker will go on to describe is an imaginary one, taking place within the speaker's mind.
In this dream, the speaker recalls "wander[ing] by the way." As the speaker moseyed along, "Bare Winter suddenly was changed to Spring." In other words, the stark, barren emptiness of winter suddenly gave way to the lush growth of spring.
Alliteration adds musicality to these opening lines and draws attention to important words. The /w/ sounds in "wandered" and "way" emphasize the speaker's leisurely, meandering steps. The gentle sibilance of "suddenly," "Spring," and "steps," meanwhile, helps to convey how swiftly and smoothly "Spring" arrives.
Already, readers might begin to suspect that this scene is symbolic: the speaker isn't simply describing a lovely springtime scene, but also trying to convey what inspiration feels like. "Bare Winter" evokes the uninspired mind, while the lush growth of "Spring" suggests a fertile imagination. That the transition between the seasons happens "suddenly" reflects the way inspiration can swiftly strike, while the fact that the speaker wanders, rather than charges ahead with clear purpose, hints that inspiration can't be forced. It comes in a rush or a flash, seemingly of its own volition, and one must be calmly open to following where inspiration leads.
Indeed, back in the speaker's dream, the "gentle odours" of the new season—the soft, enticing scents of all flowers, grasses, and so on—lead the speaker "astray." The delights of the imagination, this image suggests, lure the speaker from the beaten path.
These lines are written in iambic pentameter, meaning that they lines consist of five iambs (poetic feet with two syllables arranged in an unstressed-stressed pattern: da-DUM). Take line 1, for example:
I dreamed | that, as | I wand- | ered by | the way,
This steady, familiar meter suits the speaker's careful steps through his dream.