In the first two stanzas, the speaker notes that the time of day is evening, turning to night. All activity (namely human) is done, and he is alone in the countryside. The air has a "solemn stillness" - formal, serious and quiet.
The speaker then thinks on the lower classes of people who have died (the "rude forefathers" - here, rude means uneducated). These are the commoners, farmers and others with little to no money. He thinks how they will miss the simple things in life: "the breezy call of incense-breathing Morn," birds singing, the hunter's horn, the warmth of the fireplace, the company of the family's children.
The speaker reflects on the rich, noting that regardless of wealth, all lives "lead but to the grave." Even a grand tombstone will not "soothe the cold ear of Death." In short, everyone dies. The speaker is making a point that material success in life, in the end, is irrelevant; perhaps making the further point that the poor enjoyed life more substantially because they loved the simple things.
He also suggests that had these poor more opportunities to succeed in life, they may have flourished as well as the rich did. So, while their simple lives are admirable, a poor person may have wasted some talent - like a flower in the desert (ln. 55-56).
The speaker also considers that this may have been a good thing. Some people, given the opportunity to have power may have misused it: "Far from the maddening crowd's ignoble strife, / Their sober wishes never learned to stray," (73-74).
The speaker notes the cheap tombstones with misspelled words and sighs in tribute to the effort.
The speaker, here it seems to be Gray talking about himself, contemplates being in a grave himself, wondering when "some kindred spirit" will find his tombstone and wonder about his life and death. He imagines a farmer ("hoary-headed swain") remembering Gray as neither poor nor rich; rather, as a wanderer and someone who observes the world around him. The farmer then speaks of Gray's funeral.
The epitaph, given the preceding lines, seems to be Gray's epitaph, one that he might foresee for himself. He was not famous nor rich. He was born poor but was educated. In life, he was melancholy but sincere and went to Heaven. The epitaph closes, asking readers not to inquire about his merits or flaws; those are left to God.