Question: "The Meaning of Shakespeare" includes a chapter on one of only two of Shakespeare's plays to observe what? 

Context paragraphs:
Freewill Shakespeare Festival: The Freewill Shakespeare Festival, formerly known as the River City Shakespeare Festival was founded in 1989.  It is produced by the Edmonton, Alberta-based "Free Will Players" every summer from late-June to mid-July, with performances in the 1,000-seat Heritage Amphitheater in Hawrelak Park in Edmonton.  The Festival includes full-scale professional productions of two plays by William Shakespeare, as well as Camp Shakespeare, a summer drama camp for youth ages 8–16.  In 2008, the festival was renamed the Freewill Shakespeare Festival.

Thomas Jenkins (headmaster): Thomas Jenkins was the headmaster of the King Edward VI Grammar School in Stratford-upon-Avon in England starting in 1575.  As such, his claim to fame is that William Shakespeare is considered likely to have been one of his students.  No school records from the period survive; however, Jenkins is believed to have been of Welsh extraction, and a Welsh schoolmaster Sir Hugh Evans features in Shakespeare's play "The Merry Wives of Windsor".  Jenkins would have taught Shakespeare Latin grammar and literature.  It has been speculated that Jenkins taught, and awakened in Shakespeare, an interest in the legendary history of the British Isles, and as such influenced Shakespeare to create plays featuring this material, such as "King Lear" and "Cymbeline".

Cobbe portrait: The Cobbe portrait is an early Jacobean panel painting of a gentleman which has been argued to be a life portrait of William Shakespeare.  It is displayed at Hatchlands Park in Surrey, a National Trust property, and the portrait is so-called because of its ownership by Charles Cobbe, Church of Ireland (Anglican) Archbishop of Dublin (1686–1765).  There are numerous early copies of the painting, most of which were once identified as Shakespeare.  The Cobbe original was only identified in the collection of the Anglo-Irish Cobbe family in 2006, and had until then been completely unknown to the world.  Evidence uncovered by researchers at the Shakespeare Birthplace Trust led to the claim, presented in March 2009, that the portrait is of William Shakespeare and painted from life.  Many scholars dismiss this theory and have provided evidence to identify the portrait as one of Sir Thomas Overbury The portrait has been the centrepiece of two exhibitions dedicated to it: "Shakespeare Found: a Life Portrait" at the Shakespeare Birthplace Trust, Stratford-upon-Avon, from April–October 2009 and "The Changing Face of William Shakespeare" at the Morgan Library and Museum, New York, from February–May 2011.  An illustrated catalogue provides details of the painting and its provenance.

The Meaning of Shakespeare: The Meaning of Shakespeare (1951) was written by Harold Clarke Goddard.  A chapter is devoted to each of thirty-seven plays by William Shakespeare, ranging from three pages for "The Comedy of Errors" to over 50 for "Henry V".  Three additional chapters treat larger themes.

Philostrate: Philostrate (meaning "lover of battle") is a fictional character in a number of literary works, including William Shakespeare's "A Midsummer Night's Dream" (1596).  In that play, he is the Master of Revels at Theseus' court, meaning he is in charge of his lord's entertainments, making recommendations to Theseus, as well as altering the text of some of the plays performed in his court.  Shakespeare may have used this character to poke fun at play censorship in London at the time.  In early performances of the play, the actor who played this character probably also played the part of Egeus, Hermia's strict father.  There is only one scene in Act V where both Egeus and Philostrate are present, and in this scene Egeus' character would have taken all of Philostrate's lines as his own.

The Comedy of Errors: The Comedy of Errors is one of William Shakespeare's early plays.  It is his shortest and one of his most farcical comedies, with a major part of the humour coming from slapstick and mistaken identity, in addition to puns and word play.  "The Comedy of Errors" (along with "The Tempest") is one of only two of Shakespeare's plays to observe the Unity of Time (classical unities).  It has been adapted for opera, stage, screen and musical theatre numerous times worldwide.

Biblical allusions in Shakespeare: According to Dr. Naseeb Shaheen, Shakespeare, in writing his plays, "seldom borrows biblical references from his sources, even when those sources contain many references."  Roy Battenhouse notes that the Shakespearean tragedy "frequently echoes Bible language or paradigm, even when the play's setting is pagan."  Similarly, Peter Milward notes that despite their secular appearance, Shakespeare's plays "conceal an undercurrent of religious meaning which belongs to their deepest essence."  Further, Milward maintains that although Shakespeare "may have felt obliged by the circumstances of the Elizabethan stage to avoid Biblical or other religious subjects for his plays," such obligation "did not prevent him from making full use of the Bible in dramatizing his secular sources and thus infusing into them a Biblical meaning."  Milward continues that, in writing his plays (in particular, the tragedies), Shakespeare "shows the universal relevance of the Bible both to the reality of human life 'in this harsh world' and to its ideal in the heart of God."  Steven Marx suggests "a thorough familiarity with the Scriptures" is a prerequisite to understanding the Biblical references in the plays, and that the plays' references to the Bible "illuminate fresh and surprising meanings in the biblical text."  Marx further notes that "it is possible that Shakespeare sometimes regarded his own role of playwright and performer as godlike, his own book as potent and capacious as 'The Book'."  It is important to note, as a recent study points out “The diversity of versions reflected in Shakespeare’s writing indicates that ‘Shakespeare’s Bible’ cannot be taken for granted as unitary, since it consists of a network of different translations”

Christian observances of Jewish holidays: Christian observance of God's Holy Days (referred to as "God's holy days" or the "Feasts of the Lord" in the Book of Leviticus, chapter 23) is a practice evidenced since the time of Christ which transcends any one particular church or denomination.  Today, the practice includes Messianic Jews, members of the Hebrew Roots Movement, and a number of independent churches which observe them for a variety of reasons and in a variety of ways, with a variety of interpretations.  Some merely observe them for educational purposes; others, for example, those in the Restorationist Movement, are motivated by a desire to return to what is believed to be the true, original practice and beliefs of the early Apostolic church, and believe that Christianity has since been corrupted by tradition, anti-Semitism, Gnosticism, and Greco-Roman philosophy.

The Shakespeare Project: In October 1983, the Riverside Shakespeare Company, then New York City's only year-round professional Shakespeare theatre company, inaugurated "The Shakespeare Project", based at the theatre company's home on the Upper West Side of Manhattan, The Shakespeare Center.  "The Shakespeare Project" was the first major New York residency of actors from the Royal Shakespeare Company - with Edwin Richfield, Heather Canning, Christopher Ravenscroft, Jennie Stoller and John Kane (the later two from Peter Brook's "A Midsummer Night's Dream") - for a week of public workshops, panel discussions, seminars and performances at the company's Upper West Side theatre, The Shakespeare Center.  The event was launched at a luncheon in the Shakespeare Room of the Algonquin Hotel attended by Joseph Papp, Helen Hayes, Frank Rich, Gloria Skurski, W. Stuart McDowell, and members of the Royal Shakespeare Company in mid October 1983.  According to the "New York Times", over one thousand actors, students, teachers and stage directors, from the ages of 15 to 87, signed up for 22 sessions taught by some of the leading actors from London's Royal Shakespeare Company.

The Philadelphia Shakespeare Festival: The Philadelphia Shakespeare Festival is an annual Shakespearean theatre festival in Philadelphia.  Every year, The Festival produces two or three productions of Shakespeare's plays.  Starting out as the Red Heel Theatre in 1989, and changing name and purpose in 1993, The Philadelphia Shakespeare Festival is now the region’s only theatre devoted entirely to Shakespeare’s works.  In 2008/9, they engaged in intensive planning with the board of directors and cultural and community leaders and decided to re-brand and rename the company to better reflect their programming.  The Philadelphia Shakespeare Theatre now has several programs for adults and students including a lecture series featuring world-renowned Shakespeare scholars, Shakespeare School Tour which also tours in schools, and a Classical Acting Academy providing early career actors with intense classical training culminating in a free summer Shakespeare play for the public.

Supporting paragraphs: The Meaning of Shakespeare The Comedy of Errors
Answer: Unity of Time