From the example below:
On the mat.
Whether it qualifies as poetry may be rather doubtful, but it is perhaps the first and simplest piece of verse children learn when they are first discovering rhyme. It describes a simple situation which happens in many households and appears at first glance to be entirely literal. An actual cat of flesh, blood, bone, and fur sat on a real mat. I am sitting at a desk as I write these words. I am typing on a laptop computer. Literal language like this attempts to convey the physical universe into words as simply and directly as possible.
However, it is at least arguable that any writing is open to a figurative interpretation. What if the cat on the mat is a metaphor? It could symbolize repose, idleness, contentment or any number of other things. The first and simplest reason why poems are often figurative is that poems are analyzed more closely than other writing and people find figurative language in them which may or may not have been intended. If you prefer to interpret a poem in a purely literal manner, it is often possible to do so. Take one of the most famous poems in American literature:
Two roads diverged in a yellow wood,
And sorry I could not travel both
And be one traveler, long I stood
And looked down one as far as I could
To where it bent in the undergrowth;
It is perfectly possible to say:
Robert Frost describes a walk he took in a wood (which, rather surprisingly, was entirely yellow). He stood and looked down one road for a while, then took the other. The poem has no metaphorical meaning whatsoever and certainly has nothing to do with making choices in life. It is purely a narrative about walking in a wood.
Most readers, however, have not interpreted the poem in this way.
I have written mainly about metaphors here since they are some of the easiest examples of figurative languages to take literally, but it is possible to do the same with other figures of speech. Hyperbole, for instance, is often taken literally as a matter of sarcasm.