The text is letter 123 of CCXI Sociable Letters Written by the Thrice Noble, Illustrious, and Excellent Princess, the Lady Marchioness of Newcastle (London, 1664). I've reproduced the text literatim, except for changing VV to modern W.
I Wonder how that Person you mention in your Letter, could either have the Conscience, or Confidence to Dispraise Shakespear's Playes, as to say they were made up onely with Clowns, Fools, Watchmen, and the like; But to Answer that Person, though Shakespear's Wit will Answer for himself, I say, that it seems by his Judging, or Censuring, he Understands not Playes, or Wit; for to Express Properly, Rightly, Usually, and Naturally, a Clown's, or Fool's Humour, Expressions, Phrases, Garbs, Manners, Actions, Words, and Course of Life, is as Witty, Wise, Judicious, Ingenious, and Observing, as to Write and Express the Expressions, Phrases, Garbs, Manners, Actions, Words, and Course of Life, of Kings and Princes; and to Express Naturally, to the Life, a Mean Country Wench, as a Great Lady, a Courtesan, as a Chast Woman, a Mad man, as a Man in his right Reason and Senses, a Drunkard, as a Sober man, a Knave, as an Honest man, and so a Clown, as a Well-bred man, and a Fool, as a Wise man; nay, it Expresses and Declares a Greater Wit, to Express, and Deliver to Posterity, the Extravagancies of Madness, the Subtilty of Knaves, the Ignorance of Clowns, and the Simplicity of Naturals, or the Craft of Feigned Fools, than to Express Regularities, Plain Honesty, Courtly Garbs, or Sensible Discourses, for 'tis harder to Express Nonsense than Sense, and Ordinary Conversations, than that which is Unusual; and 'tis Harder, and Requires more Wit to Express a Jester, than a Grave Statesman; yet Shakespear did not want Wit, to Express to the Life all Sorts of Persons, of what Quality, Profession, Degree, Breeding, or Birth soever; nor did he want Wit to Express the Divers, and Different Humours, or Natures, or Several Passions in Mankind; and so Well he hath Express'd in his Playes all Sorts of Persons, as one would think he had been Transformed into every one of those Persons he hath Described; and as sometimes one would think he was Really himself the Clown or Jester he Feigns, so one would think, he was also the King, and Privy Counsellor; also as one would think he were Really the Coward he Feigns, so one would think he were the most Valiant, and Experienced Souldier; Who would not think he had been such a man as his Sir Iohn Falstaff? and who would not think he had been Harry the Fifth? & certainly Iulius Cæsar, Augustus Cæsar, and Antonius, did never Really Act their parts Better, if so Well, as he hath Described them, and I believe that Antonius and Brutus did not Speak Better to the People, than he hath Feign'd them; nay, one would think that he had been Metamorphosed from a Man to a Woman, for who could Describe Cleopatra Better than he hath done, and many other Females of his own Creating, as Nan Page, Mrs. Page, Mrs. Ford, the Doctors Maid, Bettrice, Mrs. Quickly, Doll Tearsheet, and others, too many to Relate? and in his Tragick Vein, he Presents Passions so Naturally, and Misfortunes so Probably, as he Peirces the Souls of his Readers with such a True Sense and Feeling thereof, that it Forces Tears through their Eyes, and almost Perswades them, they are Really Actors, or at least Present at those Tragedies. Who would not Swear he had been a Noble Lover, that could Woo so well? and there is not any person he hath Described in his Book, but his Readers might think they were Well acquainted with them; indeed Shakespear had a Clear Judgment, a Quick Wit, a Spreading Fancy, a Subtil Observation, a Deep Apprehension, and a most Eloquent Elocution; truly, he was a Natural Orator, as well as a Natural Poet, and he was not an Orator to Speak Well only on some Subjects, as Lawyers, who can make Eloquent Orations at the Bar, and Plead Subtilly and Wittily in Law-Cases, or Divines, that can Preach Eloquent Sermons, or Dispute Subtilly and Wittily in Theology, but take them from that, and put them to other Subjects, and they will be to seek; but Shakespear's Wit and Eloquence was General, for, and upon all Subjects, he rather wanted Subjects for his Wit and Eloquence to Work on, for which he was Forced to take some of his Plots out of History, where he only took the Bare Designs, the Wit and Language being all his Own; and so much he had above others, that those, who Writ after him, were Forced to Borrow of him, or rather to Steal from him; I could mention Divers Places, that others of our Famous Poets have Borrow'd, or Stoln, but lest I should Discover the Persons, I will not Mention the Places, or Parts, but leave it to those that Read his Playes, and others, to find them out. I should not have needed to Write this to you, for his Works would have Declared the same Truth: But I believe, those that Dispraised his Playes, Dispraised them more out of Envy, than Simplicity or Ignorance, for those that could Read his Playes, could not be so Foolish to Condemn them, only the Excellency of them caused an Envy to them. By this we may perceive, Envy doth not Leave a man in the Grave, it Follows him after Death, unless a man be Buried in Oblivion, but if he Leave any thing to be Remembred, Envy and Malice will be still throwing Aspersion upon it, or striving to Pull it down by Detraction. But leaving Shakespear's Works to their own Defence, and his Detractors to their Envy, and you to your better Imployments, than Reading my Letter, I rest,
Your faithful Friend
and humble Servant.