This speaker, who is both a critic and poet, just oozes with ambition. With "Sound and Sense," he happily jumps into a major critical debate about the role of nature (think "natural talent") and the role of art (think "practice makes perfect") in writing great poetry. He also attempts to be the poet that can employ these rules with ease. He name-drops great classical (a.k.a. ancient Greek and Roman) poets like Homer and Virgil and implies that he has these guys' skills. Neoclassical poets like Pope imitated classical poets as both a way to honor them, as well as a way to declare their own ambition to enter the literary world.
The speaker's voice may seem distinctly original at first, but the echo of the ancient poets, as well as that of the contemporary poets the speaker seeks to teach, creates a poly-voiced speaker who revels in imitation.
The couplet form structures the poem according to the logic of an echo, which shows that imitation can be the basis for good poetry.