altar, sword, and pen, Fireside, the heroic wealth of hall and bower Have forfeited their ancient English dower Of inward happiness. (3-6)
"Pen" here stands in for literature on the whole – Wordsworth puts literature up there as one of England's great traditions, along with things as important as religion and military might.
Thou hadst a voice whose sound was like the sea: Pure as the naked heavens, majestic, free (10-11)
Here, Wordsworth means Milton's poetic voice. The wild, natural imagery of these lines emphasize the tremendous power and vast scope of Milton's work.