True Ease in Writing comes from Art, not Chance, (1)
The poem declares from its first line that it is explicitly about writing. Specifically, it is about how to write with ease or grace. When we hear the word "writing," we immediately think about words on a page, but by the end of the poem we are told to "hear" a "Lay" or song. The lesson in writing becomes a lesson about hearing and about how to listen to (and by implication read) well.
But when loud Surges lash the sounding Shore,The hoarse, rough Verse shou'd like the Torrent roar. (7-8)
The speaker continually highlights the fact that he's talking about writing. Though we might think we are in the middle of a stormy sea, the word "Verse" sticks out and pulls us back into the discussion on writing. He does this in line 6 with "Numbers," line 10 with "Line" and "Words." These word choices tell us that the speaker is really talking about the basic units of a poem – the number of words that make up a line and verse – as the backbone for creating sound in a poem.
Hear how Timotheus' vary'd Lays surprize, (13)
"Vary'd Lays" are the heart of the matter for the speaker. The first line of the poem tells us that they are created from "from Art, not Chance," yet their variation leads to surprise, something we might think only chance could produce.