"Song for St. Cecilia's Day" (1687)
John Dryden

St. Cecilia was a martyr the patron saint of music.  The English marked St. Cecilia's Day (November 22) with a service & a concert.  Dryden wrote this for the 1687 concert.  It was put to music by G. B. Draghi & later by Handel.
1 "heavenly harmony" refers to the music of the spheres.  The earth was surrounded (framed) by spheres.  The moon was in the  innermost, and each sphere held another planet until the outer sphere, which held the stars.  The angels moved these spheres with their singing, the "music of the spheres."
                    "a heap 
Of jarring atoms lay."
the world was in chaos.
5 a reference to creation
6-7 The terms  refer to the 4 elements.  The music creates the world from chaos. 
cold earth
hot fire
moist water
dry air
Singing is a form of speaking, so Dryden's assertion that heavenly music created the universe is an extention of Gen. 1 & John 1, which depict God as creating the universe through his word
15 Diapason = the whole musical scale, from the highest note to the lowest.  It is an illustration of the great chain of being.  Man, being created last, completed the chain.
16 The second stanza moves from celestial to terrestrial harmony.  Human music started with Jubal (Gen. 4:21). 
24 This line sets up the next several stanzas.  Music arouses passions within us.  He then goes on in the following stanzas to catalogue the types of music and their respective passions. 
Stanza  Instrument Emotion
trumpet war
flute love
violin disdainful dame's passion.
organ worship
45-51 Orpheus was the greatest pagan musician, whose music was so beautiful that the trees uprooted and followed him.  He went to the underworld to bring his wife back from the dead.  Commanded not to look back at her, he did so anyway, so she was not able to return to life. 

St. Cecilia's music was superior to Orpheus'  because it brought the angels down from heaven because her music sounded so much like the music of the spheres. 

Note how Dryden here merges the two types of music - the celestial & the terrestrial.