A major part of the Mussaf Davening on Yom Kippur, is known as the “Avoda” service. There is a detailed description of what took place in the Beit Hamikdash on this holy day.
The main focus was on the Kohein Hagadol, and how he carried the burden of all of Am Yisrael. Fifteen different animals were sacrificed on that day, and three different confessions were made by the High Priest.
This was the only day of the year that anyone was allowed to enter the Holy of Holies. The Kohein Hagadol had to prepare himself for seven days for the great task that awaited him. He needed to maintain the highest level of spirituality as he met Hashem face to face.
Perhaps the most moving part of the service of the day, was hearing the High Priest utter the holy Name of G-d, as he did each of the three confessions. He prayed for his personal family, all of the Kohanim, and all of Klal Yisrael.
Those present in the Temple courtyard, would bow down on their faces, to acknowledge the sanctity of the moment. We bow three times during Mussaf when this story is told. We bow a fourth time when עלינו is said.
The Machzor describes the awesomeness of Yom Kippur in the Temple. It further describes the glowing face of the Kohein Hagadol, and the collective joy, after having succeeded in his mission.
Happy are those who witnessed those incredible. How sad we are, that we are only able to read about this great event. If we long for the rebuilding of the Temple, perhaps we will one day witness what our ancestors were able to experience. Gmar Chatima Tova.