Having established earlier in his commentary that Revelation 2:9 is saying that you gotta watch out for bad Christians and Christians in name only, who may as well be all the bad bits of Sodom and Egypt, we move along to quotes about what the new Ten Plagues of the new bad Egypt would be.
I don’t know who this particular quote source is, but whoever he is, this guy’s not out to make friends in academia. Plague One is philosophers who make “slippery and erratic” arguments, and Plague Two is bad songs of the poets. (That would be the plague of loud croaking frogs, for those of you playing the home game.)
There’s several pages of this. Following on his picked quotes about how even Bible study can be bad for your character if you don’t accompany it with obeying God, good works, and plenty of humility about your skills; and how being a monk could potentially be the road to Hell unless you do it right; you can tell that good ol’ St. Beatus wasn’t overly concerned with flattering his potential readers.
So yeah, if you hear any particularly bad music during this Holy Week (or Passover, for other folks), you can always amuse yourself by regarding it as a plague of frogs. Rrrrrribbit.