The metaphors in the poem's first lines present feelings as tangible, physical things. In doing so, they evoke the joy of having a living body.
The dead, the speaker remarks in the first line, once enjoyed the rich texture of all kinds of emotions. Their "hearts were woven of human joys and cares." The image of weaving here immediately suggests that this poem won't just be dealing with the pleasures that the dead have to leave behind, but with the whole human experience. "Joys and cares" are knitted together here: you can't have one without the other. In fact, this metaphor suggests, the complex texture of interwoven happiness and sadness is part of what's great about being alive.
There's a similar sense of mingled pleasure and pain in the next line, where the speaker says that the dead's hearts were "washed marvellously with sorrow." Sadness, here, is both cleansing and miraculous. This "wash" of sorrow vividly evokes what it feels like to experience a rush of sadness, like a liquid washing across one's heart. It also suggests that sorrow can feel like being washed clean, refreshed. How "marvellous[]," the speaker suggests: how strange and wonderful it is to experience sadness!
Emotions, these metaphors suggest, aren't just intellectual experiences, but bodily ones. Part of the delight of being alive is getting to feel.
(Besides these metaphors, the poem also uses plenty of personification. Read more about that in the separate "Personification" entry.)