| Quote #4
First and last being long, middle short, Amphimacer
The image of a "high-bred Racer" totally fits the amphimacer. Like a "thundering" "racer," the lines themselves "race" – and loudly. Line 9, for example, doesn't even bother with real verbs. The speaker just says "middle short" and "first and last being long" rather than, say, "the middle is short" or "the first and last are long."
| Quote #5
If Derwent be innocent, steady, and wise,
The speaker says the future poet, his son Derwent, must be a lot of things; the emphasis on "delight" in particular is important. The poet cannot just "like" nature or "enjoy" it. He must "delight" in it, which suggests something more joyous than any old pleasure.
| Quote #6
With sound sense in his brains, may make Derwent a poet – (14)
The phrase "sound sense" doesn't just mean that the speaker has "good sense," but also "a sense of sound." So in order to be a great poet, you've gotta get the rhythms down first.