This is a very interesting poem. Emily Dickinson starts by contemplating the corn being cut in Summer and thinking about nature. However, this leads her to compare what she sees with our own lives and to contemplate the two ages that we experience as humans. Note how the third stanza makes this link clear when she says:
Two Seasons, it is said, exist —
The Summer of the Just,
And this of Ours, diversified
With Prospect, and with Frost —
"The Summer of the Just" obviously refers to the afterlife that Christians have to look forward to, and the other "Season" that exists is our present one, that is characterised by "Prospect" and "Frost," obviously symbolising the opportunities but also the hardships that we face. However, the final stanza makes clear the point of the poem. As the speaker of the poem considers both of these "Seasons," she considers their relationship to each other:
May not our Second with its First
So infinite compare
That We but recollect the one
The other to prefer?
Viewed from the second season, we will remember the first season but only so we can appreciate the way that the second season compares so much better with the first. The speaker thus moves us to a time beyond the first season of our lives on this earth, just as the reaping of the corn makes her think of the different seasons, and she thus compares the two different seasons of our lives and wonders how we will think of our lives here and now when we are enjoying the afterlife.