Repetition
Your mom trying to wake you up for school: "Time to get up. Time to get up! TIME TO GET UP!"
Notice a pattern? Whenever someone really wants you to do something, they have a tendency to tell you over and over—especially if you're face down in bed pretending to be dead.
The speaker in this poem's got the same strategy. He really wants Corinna to come a-Maying, but she's showing no signs of quitting the zzzzz's. His repetition of command words like "get up" and "come" drives home his urgent message. Take a look at the first stanza, where he hits us with three "get ups" in five lines:
• "Get up, get up for shame" (1)
• "Get up, sweet slug-a-bed" (5)
"Come" plays the same role in the third stanza with an impressive five appearances. She must be getting the message!
• "Come, my Corinna, come; and, coming, mark" (29)
• "Come, we'll abroad" (39)
And, to round it out:
• "But, my Corinna, come, let's go a-Maying" (42)
Stanza 4 offers a barrage of "many", emphasizing that there's a lot of stuff going down at this May party and Corinna is missing it all. Many people are having sex, many are getting married, many are lounging in deck chairs and swapping dirty jokes. The point is to infect Corinna with a serious case of FOMO. Hear that, Corinna? So much fun happening without you!
Alliteration
Herrick also sprinkles in a good handful of alliteration—words that start with the same sounds. These guys are meant to prick up your sonic ears, drawing attention to a particular line or idea. In lines 43 and 47, for instance, alliteration points out two aspects of this May Day party: its celebration of youth and physical pleasures. First off we've got every "budding boy" (43) and then "cakes and cream." Food and sex is where it's at, according to our guy.
Herrick goes for a similar effect in stanza 4 with a luscious line-up of l-sounds:
all love, all liking, all delight
Lies drowned (67-68)
Technically, these aren't all alliteration, since the l's appear in the middle and at the ends of words (that's consonance, yo), but the overall effect is the same: a kicked-up contrast between all the fun of life and all the boredom of death. As your tongue lingers over those sweet-sounding l-words, you start to think, Gee, maybe I don't want to drown in endless night. Maybe I will have fun today!
Assonance
Assonance, which is the repetition of vowel sounds in two words, doesn't occur as often as alliteration. But when it does, it packs a punch. Consider line 59 where the long o-sounds in "grow old" emphasize how close death really is. Line 62 does the same thing:
does the sun (62)
They don't look the same, but hear how those dull u-sounds bring out Corinna's sad fate? It's all medicare and heart medicine from now on.