These lovers are engaging in the old-fashioned practice of carving each other's names into tree bark. But why is Marvell describing this as "cruel"? It seems harmless enough, right?
• In line 21: a-ha! There's something these lovers don't know about what they're doing. Either that, or they know and choose to ignore it.
• According to Marvell, the cruelty is a result of a lack of appreciation. The lovers are too busy wooing their women to notice that their totally clichéd romantic gestures are destroying something that's far more beautiful than their ladyloves. Being attracted to women, apparently, is for ignoramuses. Trees are the new ladies. You get the picture.
• As you might have expected, our speaker is not going to fall into the same trap. "Fair trees!" he apostrophizes, if anyone ever catches me carving anything into your bark…
• They'll only find a big heart with "I