The High Priest's special garments are described in detail in the chapter called Tetzaveh. A fascinating ornament he wore was the interspersed golden bells and material pomegranates he wore on his hem. The Torah explains that he was to wear these so as to make a sound when he entered the Sanctuary. If he does so, he will not die. The implication being, if he fails to wear these bells that make the noise, he will die if he thus enters the Sanctuary.
That's a pretty unusual arrangement! According to the Sages, this was to avoid the jealousy of the angels, who are jealous that man has such a Sanctuary. Why do bells help?
A further question is asked by the Netziv of Volozhin: The other Kohanim (priests) entered the Sanctuary on a daily basis as well, yet they do not have bells on their hems. Why is this danger specifically for the Kohen Gadol, the High Priest?
Oznaim Latorah explains the principle that whomever is more holy or great, has a bigger evil inclination. Thus, an ordinary Kohen is not in the same danger that the High Priest is. How so? What is the danger? And how do the bells alleviate it?
I believe the danger is the most destructive of all character traits: Pride. A great person is easily tempted to become prideful, and, as King Solomon said, "Pride comes before the fall."
It is like a ladder. The higher up one goes, the less forgiving a fall becomes. From the top of the ladder, the fall can be fatal. From one step up, it's nothing. The High Priest, as the title implies, is high up on the ladder. Thus me must remember that he is on a ladder to begin with. If he keeps that in mind, he will be careful to not take chances. He will remember where he is, and act and think accordingly. God is the "Yodea Machshavot," the Knower of Thoughts.
It also reminds me of a dog's collar, where the jingling of the bells lets the master know where the animal is a any time. It symbolizes subservience, and that is exactly what is more demanded from the greater person.
So as we strive for greatness, let us remember to couple it with ever greater humility. We may be smarter, faster, richer and so forth than our neighbors, but we are no more important than them. Let us never forget that. Each soul is created in the image of God and is holy. A person's holiness cannot be measured, thus it must not be treated with disrespect.