Lines 19-40 Summary

Lines 19-24

The rest to some faint meaning make pretence,
But Shadwell never deviates into sense.
Some beams of wit on other souls may fall,
Strike through and make a lucid interval;
But Shadwell's genuine night admits no ray,
His rising fogs prevail upon the day:

• Back to the realm of nonsense, where Shadwell is undeviatingly daft and impenetrably dense. No beam of intelligence or wit can reach him in his "genuine night." In other words, he's a complete moron. 
• Here, the irony present in Dryden's mock-heroic style becomes especially clear. Dryden drops insult after insult, berating the intelligence and substance of his victim—but in the lofty language and style that might be used to exalt the many virtues of a Homeric hero.

Lines 25-32

Besides his goodly fabric fills the eye,
And seems design'd for thoughtless majesty:
Thoughtless as monarch oaks, that shade the plain,
And, spread in solemn state, supinely reign.
Heywood and Shirley were but types of thee,
Thou last great prophet of tautology:
Even I, a dunce of more renown than they,
Was sent before but to prepare thy way;

• Nope, you didn't read that first line wrong: it's the seventeenth-century equivalent of a fat joke.
• He's thoughtless as an oak, Dryden (using a simile) says of Shadwell. We guess he probably had more intellect than a tree, but either way—ouch. 
• Dryden then references two earlier English poets and playwrights: John Heywood and James Shirley. Neither of these two writers garnered much acclaim during their day, presumably preparing the way for more lackluster writers to come. 
• A "tautology" is basically just a redundancy, the unnecessary repetition of information. Dryden accuses these poets, most importantly Shadwell himself, of bad, illogical writing.

Lines 33-40

And coarsely clad in Norwich drugget came
To teach the nations in thy greater name.
My warbling lute, the lute I whilom strung
When to King John of Portugal I sung,
Was but the prelude to that glorious day,
When thou on silver Thames did'st cut thy way,
With well tim'd oars before the royal barge,
Swell'd with the pride of thy celestial charge;

• Well, it looks like some definitions are in order here. A "drugget" is a rough woolen fabric.
• Norwich was the largest city in Norfolk County, Shadwell's place of origin. 
• "Whilom" is an archaic term for "once," as the speaker once played lute (a stringed instrument pictured here) for King John of Portugal. Dryden actually spent some time in Portugal, having written a number of pieces dedicated to the Portuguese monarch. 
• The river Thames runs through London. 
• In this section, the speaker addresses Shadwell directly in the second person, remembering as the writer appeared in the capital aboard a ship on the river ("thou on silver Thames").