Between my finger and my thumbThe squat pen rests; (1-2)
Right away we get an idea of who, or at least what, the speaker is (a writer). So that's something, right?
My father, digging. I look down (5)
And right away, we know what occupies his mind. The speaker's identity is totally shaped by how he sees his father.
Bends low, comes up twenty years away (7)
Now we can see further into the past, to where the speaker's identity began to take shape as a young boy, helping out his old man in the potato fields.