Masechet Tamid, Chapter 3, Mishnah 7. This chapter has been tracking the order of the morning avodah step by step, and the mishnah before ours left the kohanim at the moment of entering the Heichal. It described the narrow side door they used and the odd arrangement that secured it: two separate locks, the second of which the kohen could release only by pushing his arm into a slot cut in the wall. Our mishnah finishes the account. It tells us the route the kohen followed once he was through that side door, and how, from within the building, he threw open the great gate. Why the detour was needed is clear: the Heichal's principal entryway was barred from inside, so nobody standing in front of it could open it, and it had to be reached from within by another way.
"Ba lo lifshpash hatzfoni" - he arrived at the northern wicket. The kohen in question is the one whose lot had assigned him the clearing of ashes from the Mizbeach Hapenimi, the golden altar standing inside. He made his way to the area in front of the Heichal and headed for the little door set into the wall on the northern side of the great gate.
"Ushenei pishpashin hayu lo lashaar hagadol" - the great gate had two wickets, small doors built alongside it, "echad batzafon ve'echad badarom" - one on its northern flank and one on its southern flank. The phrase "shaar hagadol" is the term for the principal entryway of the Heichal, and these two modest openings stood to either side of it.
The Southern Doorway That No One Ever Used
"Shebadarom lo nichnas" - as for the southern wicket, there was no entering, "bo adam me'olam" - by any human being, at any time. It was simply never opened. "Ve'alav hu meforash" - and about this very door there is an explicit statement, "al yedei Yechezkel" - through Yechezkel Hanavi. Hashem tells him: "Hashaar hazeh sagur yihyeh" - this gate is to remain shut, "lo yipatei'ach, ve'ish lo yavo vo" - it shall not be opened, and no man shall come through it, "ki Hashem Elokei Yisrael ba vo, vehayah sagur" - for Hashem, the God of Israel, came in through it, and so it shall stay closed. That entrance was reserved, so to speak, for the Shechinah, and it therefore remained permanently locked. The wicket in actual service was consequently the one on the north.
The Route Inside
"Natal et hamaftei'ach ufatach et hapishpash" - he took the key and opened the wicket. Standing in the Ulam, the entrance hall outside the Heichal proper, the kohen used the key on the first lock of the northern doorway, and then dealt with the second lock in the manner described in the previous mishnah, reaching his hand through the wall to release it.
"Nichnas lata" - he went into the ta, the cell. Once past the wicket he followed a corridor that brought him into a small chamber built along the northern flank of the building. "Umin hata el haHeichal" - and from that chamber inward: he turned to the south and continued through a further passage that opened into the Heichal proper. "Ad shehu magia leshaar hagadol" - walking on until he stood at the great gate.
"Higia lashaar hagadol, he'evir et haneger ve'et hapotachot ufetacho" - having reached the great gate, he drew back the bolt and released the locks, and opened it. All of this was done from the inside, which is precisely why the whole roundabout route was necessary.
Two Sets of Doors
The great gate stood in the center of the eastern wall of the Heichal, and it had two sets of doors set one behind the other within the thickness of that wall, one set toward the western side and one toward the eastern side. The kohen, now standing inside the Heichal, first opened the inner doors on the western side, and then went on to open the outer doors on the eastern side.
These descriptions are genuinely hard to picture from words alone. If a good diagram or floor plan of the Beit Hamikdash is available, it is well worth studying alongside the mishnah, since the text is describing very precise architectural details.
The Signal for the Shechitah
With both pairs of doors standing open, the Heichal was fully unsealed. "Velo hayah hashochet shochet" - the kohen appointed to perform the shechitah did not begin, "ad sheshomei'a kol" - until the moment he heard the sound, "shaar hagadol sheniftach" - of the great gate swinging open. That noise served as his signal to slaughter the korban Tamid, and if a Tamid was slaughtered while the doors of the Heichal were still shut, it was invalid.