As holy zeal is the fervency of our grace, so sinful zeal is the intention and fervency of sin.
Fervency in prayer by the power of the Holy Spirit is a good preservative against thoughts rushing in. Flies never settle on the boiling pot.
To see the dull indifference, the negligent and thoughtless air that sits upon the faces of a whole assembly, while the psalm is upon their lips, might even tempt a charitable observer to suspect the fervency of their inward religion.
Praying without fervency is like hunting with a dead dog.
If the modern spirit, whatever that may be, is disinclined towards taking the Lord's word at its face value (as I hear is the case), we may observe that Isaiah's testimony to the character of the masses has strong collateral support from respectable Gentile authority. Plato lived into the administration of Eubulus, when Athens was at the peak of its jazz-and-paper era, and he speaks of the Athenian masses with all Isaiah's fervency, even comparing them to a herd of ravenous wild beasts.