Stanzas 3-4 Summary

Get out the microscope, because we’re going through this poem line-by-line.

And I will make thee beds of roses,
And a thousand fragrant posies,

Now the speaker is talking about making things, beds of flowers in this case. Wait a second—beds of flowers… flower beds… do we smell a pun in the oven?
But wait. There's more. Marlowe is also making a pun on the phrase "a thousand fragrant posies". Posey is a Renaissance-era word for bunches of flowers, but in Marlowe's day, it was also another name for poetry, or posies. This double-meaning allows line 10 to be read in several ways: the speaker is planting flower beds, the speaker is making beds out of roses and bunches of flowers, the speaker is making beds out of roses and poetry, or the speaker is making beds of roses and is also composing thousands of "fragrant" poems.
Yikes. That's a whole lot of meaning packed into one tiny line. Do these different readings change what we think of our speaker? We'll let you decide.
If you've ever used the phrase "no bed of roses" to describe a particularly nasty homework assignment, congratulations—you are quoting Marlowe. In the poem, Marlowe seems to be referring to an actual bed made of rose petals, but "bed of roses" as an expression has come to mean something more like a super luxurious or easy situation.
Also, we have to say it: roses = sex. Okay not all the time, but it's a pretty safe bet that if you're reading about roses, especially beds of roses, someone's got lovin' on the brain.

A cap of flowers, and a kirtle,
Embroidered all with leaves of myrtle.

These lines reveal more promises from the speaker. We're starting to see a trend. The speaker is clearly going to lots of trouble to promise nice things in an effort to persuade the addressee to accept the whole "come live with me, and be my love" offer.
Why are so many promises necessary? You didn't hear it from us, but it sounds like someone might be afraid of getting rejected.
Our speaker is quite the sewing machine, now promising to make caps, or hats, of flowers and a kirtle, or skirt, that is embroidered with myrtle leaves. The earthy, floral material being used to make the clothes is in keeping with the pastoral theme that was established in the previous quatrain.
We're also picking up on some potential Garden of Eden vibes, what with the "trees for clothes" talk going on.

A gown made of the finest wool
Which from our pretty lambs we pull,

Our speaker is still going on about clothes; now he's making a gown from lambs' wool, and not just any lambs' wool—the finest and best lambs' wool, freshly plucked from all those lambs living the dream up by the river with the waterfalls in stanza 2.
Clothes are everywhere in this stanza and it's not because our speaker has gone on a shopping spree. Instead, Marlowe has now started playing around with a poetic device called blazon. Blazons are a kind of poetry in which the speaker of the poem praises another person, usually a woman, by singling out different parts of her body and using metaphors to describe how beautiful and awesome they are.
Of course, this isn't a typical one, since we don't know anything at all about whom he's speaking to, but it fits the general mold. For a famous and more traditional example, check out Shakespeare's Sonnet 130.

Fair lined slippers for the cold:
With buckles of the purest gold.

In lines 15 and 16, our speaker is still in blazon mode. We have fuzzy slippers to keep toes warm and toasty in the winter, complete with snazzy gold buckles.
Here, the idealism of the pastoral really starts to get away from our speaker. Sure, it's feasible that a shepherd could make wool gowns, warm shoes, and hats of flowers, but buckles of gold? Those don't exactly pop up at random in the countryside.
And frankly, they sound really impractical for a pair of slippers.