Seamus Heaney's poem "Digging" has a lot going on in its 31 lines. One of the themes Heaney explores in the poem is how ideas and values get passed down through the generations of a family – family heritage.
The speaker narrates the poem as a member of the youngest generation of the family, a modern man who can look back and respect the hard work his father and grandfather put into their survival and livelihood. He describes their dedication to hard work in detail, when watching his father work:
"his straining rump among the flowerbeds
Bends low" (ln 6-7).
The speaker also recalls what a diligent worker his grandfather was, bragging:
"My grandfather cut more turf in a day
Than any other man on Toner’s bog" (ln 17-18)
and recalling a time when he was a little boy and brought his grandfather milk as he worked in the fields:
"He straightened up
To drink it, then fell to right away" (ln 20-21).
In this last quote, the grandfather barely pauses to take a sip of milk before diving back into his work. Clearly the speaker admires and respects his father and grandfather as dedicated workers and claims their labor as a family trait.
Another aspect of the speaker's family heritage is the type of work done. Both the speaker's father and grandfather worked with their hands out in the fields. The grandfather cut turf (ln 19), also known as peat, which was dried and used as fuel for rural Irish families. His hard work was literally keeping his family alive. The speaker's father grew potatoes (ln 8-9) and so also directly contributed to the family's basic needs.
The speaker, though is different. He values hard work, but the type of work he does is not manual labor out in the fields. As he puts it:
"But I’ve no spade to follow men like them" (ln 28).
In other words, he lacks something his father and grandfather both had; some inner strength maybe, or the need to either work or die. Whatever it is that the speaker lacks, it is symbolized by his tool. Instead of a spade, the practical tool of a laborer, the speaker has a pen. Still, he says,
"I'll dig with it" (ln 31),
suggesting that even though his labor is not back-breaking and even though it isn't necessary for survival, he will put the same energy and dedication into his work that his ancestors have put into their own.