From low to high doth dissolution climb,
And sink from high to low, along a scale
Of awful notes, whose concord shall not fail;
A musical but melancholy chime,
The phrase “low to high” can have multiple meanings. “Low to high” can be speaking of social standing; generally the more wealthy are less likely to perish. The phase can also depict the motion of the sun in the day–it rises, then sets. 
 Dissolution: end, decomposition, or death. For dissolution to “climb” gives this line an ominous quality and builds suspense.
Mutability