Quatrain 3 Summary

Line 9

Time doth transfix the flourish set on youth,

• Quatrain 3 is all about focusing our attention on big bad Mr. Time and showing just what a terrible dude he is.
• Just look what he does: he "doth transfix the flourish set on youth." Wait… what? 
• The word "transfix" has a pretty straightforward meaning—to pierce or bore through something. As for "flourish," it does have a wider range of meanings, but most of them are in the general ballpark of blooming, blossoming, and, well, you get the idea.
• The problem is what happens when you put them together. What do you get then?
• Hard to say, but it definitely sounds bad. The basic idea? Time destroys youth's glory, beauty, whatever. Time pierces right through all the nice stuff and ruins…absolutely everything. 
• Another important thing to notice in Line 9 is how it starts to introduce imagery from the natural world of growth and decay. It happens pretty subtly here—in the one word "flourish"—but nature (and also agricultural) imagery will continue to pop up so keep a weather eye out for leafy greens.

Line 10

And delves the parallels in beauty's brow,

• If the imagery of Line 9 was a little hard to pin down, the imagery in Line 10 couldn't be clearer. 
• The only word you might not know here is "delve," meaning dig. Usually, we use the word "delve" to mean especially serious or deep digging. You can kind of get a sense from this just from the way the word sounds—with those drawn-out "l" and "v" sounds. (Say it out loud to yourself—see what we mean?)
• Once you get past that, though, the imagery here is pretty spectacular. You've probably learned the concept of parallel lines in math class, but chances are you learned a pretty abstract definition like "two straight lines that never touch." Shakespeare's genius is to take that abstract word and use it as a metaphor for something concrete, something you could "delve" or "dig." 
• Any guesses what he's talking about? That's right: the trenches cut in a field by a plow or harrow, which are always parallel.
• But wait—these parallels aren't being dug in a field… they're being dug in "beauty's brow." What's the deal?
• Well, ladies and gentlemen, it looks like we've got ourselves here a good old-fashioned case of metaphor. Without explicitly telling you that he's making a comparison, the way this poetic line is structured makes you see a parallel (oh, we're so clever with the puns) between a field and somebody's forehead.
• So, what are the parallels in a forehead? The lines and wrinkles created by old age, a.k.a. by time—who, as you may remember from Line 9, is the one doing the delving. 
• Cool. So Shakespeare is saying that time destroys beauty by carving wrinkles into people's foreheads. That may not sound so nice… but it's about to get worse. Don't say we didn't warn you.

Line 11

Feeds on the rarities of nature's truth,

• According to our speaker, time destroys—make that devours—the best things ("rarities") in nature. That's definitely a lot more intense than the wrinkles on the forehead we learned about in Line 10. 
• Literally translated, the idea here is that time "feeds on," (or consumes, destroys" or whatever synonym you feel like sticking in) the most rare and valuable things in nature's reality, or "truth." So we're continuing with the whole all-things-green motif that was set up by the agricultural imagery of Line 10.

Line 12

And nothing stands but for his scythe to mow.

• Well, it definitely looks like the speaker has reason to be agitated. This perhaps the most disturbing image in Shakespeare's entire poem.
• Did it occur to you, back in Line 10, that all that imagery of plowing and harrowing (i.e. "delv[ing] parallels") could be read in a more hopeful way? After all, when people go out with their tractors (or, in Shakespeare's day, oxen or draft horses), they aren't just tearing up their fields for the sake of destruction. No—they're doing it to put seeds in the ground so that new life can come up. 
• In Line 12, however, it looks like the speaker of Shakespeare's poem knew you were thinking that—and decided that that was just too much hopefulness.
• Sure, he tells us, new life does come up like wheat out of the ground, but then time just comes along and cuts it down with his scythe. 
• What makes this line especially disturbing is how universal it is. According to the speaker, there is literally "nothing" that will escape the destruction of time.
• Yikes.