"The Man with the Hoe" is a poem that questions the power differential in society and how those with power treat those without.
To understand the second stanza, one must start with the epigraph:
God made man in His own image,
in the image of God made He him. (Genesis)
Following this biblical reference, the first stanza paints the image of a downtrodden farmworker. There is a striking contrast presented by these two ideas. The epigraph presents the idea that humans are made in the image of god, or that we are like god (or divine) ourselves. The second presents a very un-deified image of humanity: an overworked farmworker, dead in his tracks.
The second stanza confronts the reader with the discrepancy between the two. Consider the exasperated first line: "What gulfs between him and the seraphim!" Here, the author is pointing our attention to the distance between the dead farmer and the seraphim, or angels. The list of rhetorical questions that follows underscores the joyful aspects of life that the farmer is deprived of due to his socioeconomic status: music, the loveliness of the sunrise, the blossoming of flowers.
From there, the narrator steps back to compare the dead farmer to all of us:
Through this dread shape the suffering ages look;
is in that aching stoop....
Basically, the narrator is suggesting that all of human suffering is bound up in this dead farmworker and that time will inevitably treat all of us the same way this farmer has been treated. It is, admittedly, a bleak outlook. But the author uses this image as a call to arms, to inspire those in power to create a better quality of life for the downtrodden.