Answer:
The valuable things in life are often concealed by less important matters.
Step-by-step explanation:
Remember, from the passage Melantha was going to participate in a festival that would involve "her and the other girls her age....leaving their toys [valuable things] before the statue of Artemis, showing they no longer needed childish things."
However, Melantha had a rethink and she decided to keep it [The Clay Horse], thus it shows that valuable things [the clay horse which is attached to her hapiness] are often concealed by less important matters [the festival].