This very short dialogue of Plato's explores the difference between art (understood here as human skill or talent) and divine inspiration in poetry.
Socrates approaches a renowned reciter, Ion, who specializes in Homer. This specialty allows Socrates to question Ion about his ability, which he quickly acknowledges is limited to Homer, rather than applying to all poets equally. Using his famous questioning technique, Socrates is quickly able to lead the reciter to admit that one who is truly skilled and knowledgeable in the art of poetry would be able to assess the relative skill of poets and thus be able to speak on any poet, not just one.
Additionally, while Ion can recite passages from Homer that refer to chariot racing, fishing, and medicine, he admits that a driver, fisherman, and a doctor would be better able to speak to the truth of those passage than he. After having bragged about his own knowledge and skill, Ion is backed into a corner whereupon Socrates asks him to choose whether he is a liar and cheat or has been divinely inspired through Homer.
Had Ion been less sure of his own skill or been better able to discuss other poets, he would not have served Plato's purpose. Instead, he is nearly idiotic in all things save Homer. This allows Plato to make the point that all truly great poetry is divinely inspired and thus has the ability to inspire
Such as there is in that stone which Euripedes called the Magnesian, but most people call it
the Heracleian stone. This magnet attracts iron rings, and not only that, but puts the same
power into the iron rings, so that they can do the same as the stone does; they attract other
rings, so that sometimes there is a whole long string of these rings hanging together and all
depend for their power on that one stone. So the Muse not only inspires people herself, but
through these inspired ones others are inspired and dangle in a string.
When one considers Ions near idiocy (seriously, reading his "contribution" to the conversation is almost painful), this could lead to an interesting conversation on Platonic forms and their imperfect earthly copies, but as Plato saves that for another dialogue, it is more of a mental exercise that this short work almost asks for.