Symbolism, Imagery, Allegory
He's a poet, and he knows it: in the beginning of the play, the Poet tells the Painter about the poem that he's written especially for Timon. This nifty little piece of poetry is a mini-allegory of the play itself. Now, allegories have two levels of meaning, so let's figure out both from what the Poet tells us.
When Fortune in her shift and change of mood
Spurns down her late beloved, all his dependants
Which labour'd after him to the mountain's top
Even on their knees and hands, let him slip down,
Not one accompanying his declining foot. (1.1.87-91)
It looks like Fortune it totally okay with giving out wealth to people and then one deciding that—whoops—she's just gonna stop doing that. A person who's had wealth and lost it isn't going to get anything from anybody; he'll just slip off a mountain, and no one will lift a finger to help him. Uh-oh.
Now that we've got the literal meaning out of the way, let's figure out the figurative meaning. It looks like—surprise—the character in the poem is Timon himself. In case we don't immediately pick up on that, the Poet lets us right in on it: "One do I personate of Lord Timon's frame," he tells the Painter (1.1.72). And here's a nifty piece of foreshadowing: Timon will lose all his money, and none of his friends will come to help him.
Shakespeare gives us a little wink-wink, nudge-nudge with this one by letting us in on what's going to happen. It's like a big spoiler alert. Too bad Timon doesn't catch it—he's just too blind to see what pretty much everyone around him can see coming a mile away.