The first half of "There Will Come Soft Rains" is full of imagery, as the speaker describes a peaceful world untouched by humanity's violent destruction. To emphasize this sense of serenity, the speaker draws on the human senses, focusing on how "soft[ly]" falling rain will bring out an earthy smell from the ground. This creates a feeling of tranquility, inviting readers to imagine the familiar scent of rainfall and the gentle sound of water dropping on the ground.
The speaker then concentrates on sound-related imagery, referencing the "shimmering sound" that swallows make as they fly in circles in the sky. Frogs join in this natural chorus, "singing at night" (that is, croaking). This makes it even easier for readers to imagine themselves in an environment in which the only activity comes from nature itself. By describing these sounds, the speaker makes it seem like the poem's setting is full of music.
The visual imagery contributes to this sense of beauty. The speaker mentions "wild plum trees" that have bloomed a "tremulous white." The word "tremulous" suggests that the tree's white petals flutter gently in a soft breeze—a very calming, meditative image. To make the scene feel even more vibrant, the speaker notes the "feathery fire" of some nearby robins, adding a pop of color that illustrates nature's overwhelming beauty.
At the same time, it's also possible to interpret this imagery as an allusion to the horrific sights one might encounter on a battlefield. "There Will Come Soft Rains" was first published in 1918, shortly after the Sedition Act of 1918, which made it illegal to publish anti-war messages. It's possible, then, that the poem's imagery is Teasedale's subtle way of writing about the war without making overt references to it.
Under this interpretation, images like the robins' "feathery fire" seem like metaphorical representations of the explosions on a battlefield. Similarly, it's possible that the "tremulous white" of the plum trees is a reference to smoke hanging over the trenches after an explosion (or perhaps a reference to the flare of bright light one might see right as a grenade goes off). The potential double-meaning of the imagery thus hints at the juxtaposition between the natural world's calm beauty and humanity's destructive chaos.