1. Muse: a guiding spirit; source of inspiration.

2. fair: beautiful, giving promise of success.

3. As: that. —This completes the "So oft" with which the poem begins. The whole idea can be paraphrased as follows: "In my poetry I have so often invoked thee that other poets are imitating me and proclaiming that you have inspired them, too."   every alien pen: i.e., other poets.   got my use: adopted my practice.

4. under thee: under your patronage.   disperse: circulate.

5. dumb: lacking the power of speech.  on high: aloud.

6. aloft to fly: i.e., to get off the ground. —Normally, "heavy ignorance" stays on the ground, repeating clichés like chickens scratching in the dirt.

7. added feathers to the learned's wing: i.e., enabled learned poets who were already making high flights, fly higher.

8. grace: majesty.

9. compile: compose.

10. influence: inspiration.

11. mend: adjust; set right.

12. arts: literary culture; learning.   graces: pleasing qualities.

13. advance: lift up.

14. learning: advanced knowledge, wisdom.  rude: uncultivated, unlearned.