In an article for Acharei-Mot 5774, Rabbi Cherki notes that there is a danger that when the High Priest enters the holiest part of the Temple he may not want to leave the high spiritual level that he as attained.
There are three ways to enter the Holy of Holies in the Temple. One is to be like Moses, who went into the holiest area without any special preparation – not wearing priestly garments, without bringing sacrifices, and without any need to send a goat out into the wilderness. Moses is the ideal model of a man without any blemish. He does not need to mend anything before entering, and he simply hears the word of G-d emanating from between the two Cherubs.
The second possibility is to be like Aaron, and to perform the holy service described in the Torah portion of Acharei-Mot. Aaron, whose task is to bring people who are far away closer and to mend their distortions, is allowed to enter the holy area if he does all that is necessary to remove the obstacles, which are remnants left by the sins of the people. What he does is to raise up the forces of the enterprise of life, symbolized by a bull, and to separate between the tempestuous forces of the soul which are worthy of joining the holiest forces, as symbolized by the goat that is sacrificed, from the aspects of that force which must be discarded from the soul, symbolized by the goat that is sent away.
The third way to enter the Holy of Holies is that of the High Priests throughout subsequent generations. Any priest who is not Aaron himself but who has inherited his status must take advantage of a unique time that will make it easier for him to carry out the burden of atoning for the sins of Israel. This happens once every year on Yom Kippur, which is a time when atonement is especially relevant.
The yearning for sanctity, that is, the desire to reunite with the source of life, is a constant urge within the soul of man. This urge involves some danger, as was seen in the deaths of Nadav and Avihu.
Aaron's name is emphasized in the description of the labors performed in the Temple: "Speak to Aaron... Let Aaron give... Let Aaron sacrifice," and more. But in the description of entering the Holy of Holies, Aaron's name does not appear. "Let him take a full pan... Let him bring... Let him put the incense... Let him sprinkle the blood..." and so on. This is very puzzling, especially in view of the fact that nobody else is allowed to be at the site with him: "Let no man be in the Tent of Meeting, from when he comes to atone in the Sanctuary until he leaves" [Leviticus 16:17]. The only person that is there at this time is Aaron!
The answer to this anomaly must be that at that moment Aaron loses his identity, as a result of the experience that he has gone through. This is a temporary loss of identity in deference to the place where the Divine revelation took place. However, if that is the case there is a distinct possibility that the priest might not want to return to our world, after he has sampled the wonderful feeling of his own insignificance in relation to the Shechina. Such a significant spiritual uplift brings supreme pleasure to the High Priest, but it is not good for the people who sent him on a mission to bring down abundance to our world from the source of all life. And that is why it is written in the Zohar that a string would be tied to the High Priest's foot, so that he would not forget the external world which he had been sent to mend.
That is why the peak of Yom Kippur is when the High Priest leaves the Holy of Holies and not when he enters: "How wonderful it was for the High Priest when he left the holy area in peace." [Mussaf Prayer, Yom Kippur].
Source: "AS SHABBAT APPROACHES" – a biweekly column in Shabbat B'Shabbato, Acharei-Mot 5774, Volume 1520. (Zomet Institute) See: www.zomet.org.il/eng