Middos, Chapter 4, Mishnah 1. Our chapter now takes up the measurements of the Heichal. Heichal is a word that can cover the entire structure, but here the mishnah has one particular chamber in mind: the Kodesh, which had the Ulam on its eastern side and the Kodesh Hakodashim on its western side. Six amot was the thickness of the walls enclosing it, and set into the eastern one was the doorway through which a person moved from the Ulam inward into the Heichal.
The mishnah begins with the dimensions of that entrance: "Pitcho shel Heichal gov'ho esrim amah v'rochbo eser amot", the doorway of the Heichal was twenty amot high and ten amot wide.
Four Doors, Two Sets
"V'arba delatot hayu lo", four doors served this entrance. Each of them measured twenty amot in height and five amot in width, so that a pair standing side by side spanned the full ten amot of the opening. "Shtayim bifnim u'shtayim bachutz", one pair was set further in, along the inner face of the six amah wall that stood between the Ulam and the Heichal, and the second pair was set further out, along the outer face of that same wall.
What is the source for this? "Shene'emar, shtayim delatot la'Heichal v'lakodesh", Yechezkel speaks of two doors for the Heichal and two for the Kodesh. The pairs mentioned by the pasuk are to be understood as two sets of doors: the set standing nearer to the Kodesh Hakodashim, which the pasuk assigns to the Kodesh, and the set standing further away, which it assigns to the Heichal.
Which Way Each Pair Swung
"Hachitzonot niftachot l'toch hapetach l'chasot ovyo shel kotel", the outer pair opened westward, into the space of the doorway, so that once opened they rested flat against the six amah partition between Ulam and Heichal and concealed its thickness. "V'hapnimiyot niftachot l'toch habayit l'chasot me'achar hadelatot", the inner pair opened in the opposite direction, swinging into the Heichal and covering the stretches of wall that they hid from view.
Why was that significant? "Shekol habayit tuach b'zahav chutz me'achar hadelatot", gold overlaid every surface of the Heichal, apart from those strips of wall that the opened doors kept out of sight. Since nobody's eye ever fell upon them while the doors rested against them, plating them served no purpose.
The Opinion of Rabbi Yehuda
"Rabbi Yehuda omer, b'toch hapetach hayu omdot", Rabbi Yehuda offers a different picture of how the doors were set. In his description, the entrance had doorposts on both its eastern and its western side, and the doors were attached to them, with all four doors standing within the thickness of the entrance itself.
"K'min istramita hayu v'nichpalot l'achoreihen", their construction was that of an istramita, a door built of two leaves joined by hinges, so that each door doubled back upon itself. All of the folding took place inside the opening. "Elu shtei amot vachetzi v'elu shtei amot vachetzi", when opened, the outer pair took up two amot and a half of the wall's depth, and the inner pair another two amot and a half. "Chatzi amah mezuzah mikan vachatzi amah mezuzah mikan", half an amah went to a doorpost here and half an amah to a doorpost there, and that accounts for all six amot.
Rabbi Yehuda anchors his picture in a pasuk in Yechezkel: "Shtayim delatot lad'latot, shtayim musabot delatot, shtayim l'delet achat u'shtei delatot la'acheret", the doors themselves have two doors, doors that turn, two belonging to this door and two belonging to its counterpart. Since the pasuk assigns a pair of doors to each individual door, we learn that every door was composed of two leaves. And by calling them turning doors, it teaches that those leaves pivoted and folded back one against the other.
This mishnah is one of those passages that becomes far clearer once you have a diagram in front of you. Its whole purpose is to describe precisely how the four doors were positioned within this part of the Beit Hamikdash.