Apart from its straightforward entertainment value, I don't think the Linwell Theatre programme contributes significantly to an understanding of The Play itself. It sets the scene nicely (if you'll forgive the weak pun), but, like the Thick As A Brick spoof newspaper, serves only as a nice keepsake, even a marketing gimmick.
The 2003 Remaster includes the theatre programme in the booklet and on the enhanced portion of the CD.
The centre pages of this CD booklet may confuse those who haven't seen the original gatefold LP sleeve: the text doesn't fit on the page. As shown on the corresponding pages on the enhanced CD, the inside of the LP sleeve features the lyrics against a pink background, itself featuring lightly drawn theatre masks: tragedy (left) and comedy (right). Beneath all this is an embroidered ribbon saying "Jethro Tull" (left) and "A Passion Play" (right).
The theatre programme fits into the middle, tucked under two flaps to keep the pages in position. The curved edges of the flaps are visible on that page of the enhanced CD. Located correctly, therefore, the centre pages of the programme show the portion of gatefold underneath the programme, 'as if it wasn't there', and the lyrics can be read clearly.
Another promotional curiosity: the initial release (i.e. only in 1973 itself, not repressings) apparently featured not only the Linwell theatre programme, but also a real, wearable theatre mask; Job (in Australia) recalls it as having been of Comedy. Does anyone remember this? Does anyone still HAVE one?
It's been reported by those who bought the UK edition on the release date that it did not include a mask.