Lines 19-30 Summary

Lines 19-24 

My SHAKSPEARE rise ! I will not lodge thee by
Chaucer, or Spenser, or bid Beaumont lie
A little further, to make thee a room :
Thou art a monument without a tomb,
And art alive still while thy book doth live
And we have wits to read, and praise to give.

• Jonson commands Shakespeare to rise, kind of in a creepy come-back-from-the-dead way, but also in a "may your legacy rise above those of your predecessors" kind of way.
• Speaking of the dead and of Shakespeare's predecessors, starting in line 19 Jonson launches off on a tangent about why Shakespeare leaves them all in the dust.
• He mentions Geoffrey Chaucer (The Canterbury Tales), Spenser (The Faerie Queen), and Francis Beaumont (Philaster and other plays)—all British authors, all very famous in their own right, and according to Jonson, all not as good as our boy Willy.
• Literally, Jonson is talking about a tomb, specifically a little slice of England's famous church, Westminster Abbey that is commonly known as Poet's Corner. As you might have guessed from the title, Poet's Corner is the area of Westminster Abbey where famous British poets are buried or memorialized. Chaucer was the first great poet to be buried there, but Spenser and Beaumont followed closely behind. Ironically, however, at the time Jonson was writing this poem, Shakespeare had no tomb or monument in the famous church (one would later be erected, but not until 1740).
• So when Jonson says Shakespeare is "a monument without a tomb" he's being both literal (Shakespeare has no tomb in Poet's Corner) and figurative, as we see in line 23.
• Apparently Shakespeare needs no tomb because, according to Jonson, he's still alive. As long as his works live on and continue to be read and praised, Shakespeare will be a monument to drama and the English language but still "alive" because those who are living continue to read and engage with his work. 
• Given the tone of Jonson's earlier lines, it's safe to assume the author thinks this will be for a long, long time.

Lines 25-30

That I not mix thee so my brain excuses,
I mean with great, but disproportioned Muses :
For if I thought my judgment were of years,
I should commit thee surely with thy peers,
And tell how far thou didst our Lyly outshine,
Or sporting Kyd, or Marlowe's mighty line.

• Jonson's diction gets a bit foggy in the first few lines here, but it's safe to say he's still in compare and contrast mode. 
• Line 25 can essentially be paraphrased as Jonson's apology for comparing Shakespeare with people from different time periods all over the literary spectrum. Anyone who has read Chaucer or Spenser will know that, while they are great, the works for which they are famous are very much unlike anything that Shakespeare wrote.
• Jonson continues, though, as if to say, "if time period did matter, though, I could easily show how much better you were than your peers who were trying to write in the same style."
• He mentions John Lyly, Thomas Kyd, and Christopher Marlowe—all three dramatists writing during Shakespeare's time, all with very popular plays. For Jonson, however, none will command the enduring legacy for which Shakespeare is destined.