Our speaker welcomes us to the poem, which is not, she says, stuff from nature. Then the speaker reminisces about a grandfather's farm, only it's not her memory—it's the memory of whomever she's talking to. She describes the barn and the house, and everything's all cozy and nice.
Except for the fact that, as our speaker tells us, nothing lasts. Everything ends up in a graveyard someday. Including the speaker's mother and father, who seem to have had less than awesome lives. But that's neither here nor there, because our speaker loved them and wishes them well. She's not about living in the past—she wants to take responsibility for her life.
After a few reminders that this poem isn't the world and nature and all that jazz (but it does want to bloom and flower to make us feel good), the speaker tells us that all those grown-ups crying about their childhood miseries are, well, miserable lumps. So instead of feeling miserable about our lives, we should head out into the field and take a good long look at the world and the animals. We should let our grief happen, but then rise up and be happy with what we have—which is that natural world.