In the first verse of the poem, what is it that can express "A flowery tale more sweetly than our rhyme"?

You forgot to say that this question is about "Ode on a Grecian urn", by Keats.

This verse can express that the urn has the capacity to tell a better story and in a more delicate and sensitive way than a poet.

Explanation:

In the line "A flowery tale more sweetly than our rhyme" the poet is extolling the urn's ability to tell the stories he knows and keeps in a beautiful, delicate and sensitive way. This ability is greater than the ability of the poets and the urn does not need rhymes, or any other device, because this ability reflects what it is and is therefore exercised without any effort, but with grace and lightness, being compared to a flower.

i guess you are missing the idea that has to be supported, am i right?