Right away, it's clear that the "Song to the Men of England" is a polemic—that is, a piece of writing with a serious and angry point to make about the way society works. More than that, the poem is a call to arms, an invitation to revolution. And the people the speaker wants to inspire to revolt are no less than all the "Men of England."
This doesn't actually mean every single Englishman, however. Rather, the speaker addresses those who "plough" and "toil": the working classes, the laborers on whose backs English farming and manufacturing rest.
The speaker has some rhetorical questions for this group of people. Listen to the anaphora here:
Men of England, wherefore plough
For the lords who lay ye low?
Wherefore weave with toil and care
The rich robes your tyrants wear?
That repeated "wherefore" (or "why") makes it clear that the speaker has a lot of questions about the way the world currently works. Does it make sense, the speaker wonders, that one group of people should do all the work and another should enjoy all the profit (and "lay" the workers "low," treading them underfoot, for that matter)? The implied answer is absolutely not.
The speaker's musical language in this first stanza suggests that this poem is intended as a battle cry, the sort of thing that rebellious workers could chant from a barricade. Besides the insistent alliteration of phrases like "the lords who lay ye low" and "rich robes," the poem uses memorable, chant-worthy rhymed couplets: plough / low, care / wear.
Listen, too, to the meter in these first lines:
Men of | England, | wherefore | plough
For the | lords who | lay ye | low?
This punchy, stress-first pattern is trochaic tetrameter—that is, lines of four trochees, metrical feet with a DUM-da rhythm. The speaker even cuts off the last unstressed syllable of these lines, so each line both begins and ends with a stress (and a bang). This is a poem made for yelling.