The speaker wastes no time in saying exactly how they feel about publication: the poem's opening metaphor compares selling one's work to holding an "Auction," a public sale in which people try to outbid each other for goods, services, or property. But instead of selling things, this "Auction" involves selling the "Mind" itself; publication, to this speaker, is like putting a price on one's very thoughts. What's more, this metaphor implies that the desire to publish encourages writers to cater to public opinions and tastes (so that people will make higher "bids") rather than stick to whatever they themselves find meaningful.
Note how the use of alliteration and capitalization draw attention to the phrase "Mind of Man," suggesting that the speaker isn't just referring to the thoughts and perceptions of an individual writer, but to the entire idea of the "Mind" in general. In other words, when writers sell their work, the speaker believes they're actually insulting the human capacity to think and observe.
Note, too, the passionate and persuasive tone of the poem: the speaker's strong opening statement is underlined by a forceful, trochaic meter (meaning the main poetic unit here is the trochee, a foot that moves from a stressed syllable to an unstressed syllable—like the word "trochee" itself!). The first line of the poem more specifically uses trochaic tetrameter, meaning that it consists of four trochees—four DA-dums—in a row:
Publi- | cation — | is the | Auction
The second line is then written in trochaic trimeter, meaning it has three trochees instead of four. It's also catalectic, which simply means that it's missing its final syllable:
Of the | Mind of | Man —
Trochees lend the poem a driving, pounding rhythm, which that catalexis intensifies by ending the line on a stressed syllable. This pattern will continue throughout the poem.