Can you explain the following quote from "Alexander's Feast" by John Dryden with reference to the context?
"He raised a mortal to the skies, / She drew an angel down." (lines 169-70)
Alexander's Feast; or, The Power of Music:
An Ode in Honour of St. Cecilia's Day
by John Dryden
At last divine Cecilia came,
Inventress of the vocal frame;
The sweet enthusiast, from her sacred store,
Enlarged the former narrow bounds,
And added length to solemn sounds, 
With nature's mother-wit, and arts unknown before.
Let old Timotheus yield the prize,
Or both divide the crown;
He raised a mortal to the skies,
She drew an angel down. 
You absolutely must understand the context of this poem by Dryden, inspired by Edmund Spenser's earlier work, in order to understand the quotation, otherwise "He" and "She" are meaningless or, at best, confusing pronouns. "He" in this case is Timotheus, the renowned musician and lyre player at Alexander the Great's court (356-323 BC). He is not to be confused with the earlier Timotheus of Miletus (c. 450-355 BC) of the Classical era who added an additional string to the classical lyre.
In Dryden's poem, Timotheus is exquisitely performing for Alexander in celebration of Saint Cecilia's Day. On a feast day, Timoteus's duties are two-fold: he must praise Alexander and diefy him while also praising and celebrating the patron saint of the feast, in this case, Saint Cecilia. She is renowned and sainted for creating the first organ ("voice frame") and initiating Christian religious music.
Dryden chronicles how Timotheus played his lyre ("With flying fingers touched the lyre:") to exalt Alexander ("The godlike hero"); to link Alexander to the god Juno ("The monarch hears; / Assumes the god,"); to describe Alexander's Bacchanal praise and celebration ("Bacchus' blessings are a treasure,"); and to alter Alexander's moods by the choice of music played ("The master [Timotheus] saw the madness rise, / [..] /He chose a mournful muse,"):
Timotheus, to his breathing flute,
And sounding lyre,
Could swell the soul to rage, or kindle soft desire. 
Finally in Stanza VII, Cecilia herself "comes down" to the feast. Dryden alludes to her a few lines ahead of her appearance by mentioning "organs": "When organs still were mute." As you recall, Cecilia is credited with inventing the organ. Now comes the lead-in to the meaning of the quote you ask about.
Dryden has shown how Timotheus uses his lyre to create any mood he desires to see in his listeners. In other words, Dryden shows how Timotheus is the master extraordinaire of musical accomplishment. Now Dryden tells us that Cecilia "enlarged the former narrow bounds" with her "vocal frame," or organ. After hearing about Timotheus's skill, we are meant to be astounded that his music is now called "narrow bounds" (as in having less significant accomplishments) and equally astounded that his greatness could be "enlarged" upon (made greater, surpassed). Yet we are assured Cecilia has surpassed and overshadowed Timotheus's music. So it is that Dryden states that while Timotheus could elevate in praise and stir the heart of Alexander through his lyre, Cecilia could bring heaven to earth and unite the hearts of all with angels through her organ, itself a metaphoric angel:
He raised a mortal to the skies,
She drew an angel down.