Stating that a poem's speaker feels sad is one way to communicate sadness. It's rarely the way that actually makes a reader feel it. Poets rely on imagery — concrete, sensory description — and figurative language — comparisons and substitutions like metaphor and simile — to produce an emotional effect indirectly, letting a reader arrive at a feeling through a specific, vivid picture rather than being told what to feel outright.
A concrete image does work an abstract label can't
Imagery grounds a poem in specific sensory detail — sight, sound, touch, taste, smell — rather than abstract statement. Describing "a coat still hanging by the door, the collar shaped to a shoulder that isn't there anymore" does more work toward conveying grief than the word "grief" itself would, because it hands the reader a specific, physical detail to imagine and lets the emotional weight arise from that image rather than being asserted directly. This is part of why poetry instruction so often repeats some version of "show, don't tell": an abstract emotional label asks a reader to simply accept a stated feeling, while a well-chosen concrete image invites the reader to reconstruct that feeling themselves, from evidence, which tends to land with more force.
Figurative language substitutes one thing for another on purpose
Figurative language goes a step further than plain imagery by deliberately substituting or comparing one thing for another that it isn't literally. A metaphor states that one thing is another ("grief is a tide"); a simile compares two things explicitly using "like" or "as" ("grief comes like a tide"). Both devices ask a reader to carry meaning across from a source domain, often something concrete and physically familiar, onto the actual subject, something more abstract or harder to describe directly. A tide, specifically, brings with it connotations of returning, of being unpredictable in timing but inevitable in eventually arriving, of overwhelming force that recedes and leaves things changed — associations the single word "grief" doesn't automatically carry on its own, which is exactly why the figurative substitution can communicate more precisely, and more affectingly, than a literal, abstract statement of the same underlying idea.
What we're still unsure about
That imagery and figurative language function by prompting a reader to construct meaning and emotion from concrete detail, rather than by simply asserting it, is a well-established principle in literary study, supported by extensive close reading and critical tradition. What's harder to pin down with precision is exactly why certain images or comparisons land more powerfully for a given reader than others — response to imagery is shaped by a reader's own associations, cultural background, and personal experience in ways literary theory can describe in general terms but can't fully predict for any specific reader encountering any specific poem, which is part of why the same image can move one reader deeply and leave another comparatively unaffected.
This sits inside Imagery & Figurative Language, one of seven topics in Poetry, one of five domains in Literature, one of seventeen subjects the app can quiz you on.