What was in the Holy of Holies?
The answer to that question varies from era to era. During the time of Solomon’s Temple the Holy of Holies housed the Ark of the Covenant. The Ark mysteriously disappeared from the text of Scripture (and apparently from the Temple) after that time. Therefore, the Holy of Holies was empty during the Second Temple era except on Yom Kippur. On that sacred occasion the High Priest was called to engage the Lord on behalf of all Israel.
How High was the High Priest?
During Temple days, the High Priest had a sacred position. Though the individuals were not always “holy,” the position was sacred. Perhaps a note about the position of High Priest is in order.
In ancient times this position was handed down from father to son within a few priestly families . . . This tradition was undermined, to a certain extent, by the Hasmoneans, who, themselves priests, appropriated this lofty position. After the rise of the Herodian dynasty and in the days of the Roman governors, corruption was involved in the appointment of priests, and the high priesthood was sometimes awarded to people who paid enormous sums in order to purchase the honor.
The Yoma tractate of the Talmud gives the best explanation of the Priest’s duties on Yom Kippur. His position of influence varied during different times in Jewish history. It is clear that the position carried with it tremendous power. The strong leadership and tight control held under priestly rule dominated ancient Israel from 445 to 37 BCE. “During the Persian occupation and in the Hasmonean era, the High Priest was, for all practical purposes, ruler of the country.”
Caiaphas: Priest “Over” Jesus
Although Christians tend to view Caiaphas as the wicked Jewish ruler who presided over the mock trial of Jesus, they generally know very little about the position he held. The most popular fact about Caiaphas is that he was a “card-carrying” Sadducee. The other leading players within first century Judaism were the Pharisees. The New Testament writers correctly present the Pharisees as the more “orthodox” group. I do not support the view that the Jewish leaders (or the Jewish people) were inherently wicked, power-hungry, religious hypocrites. Undoubtedly, examples existed, however, I totally reject that anti-Semitic stereotype. I am convinced that for the most part, the Jewish leaders were sincere and honorable. Jesus exhorted His followers to observe the Law while seeking to exceed the righteousness of the scribes and Pharisees (Matt. 5:20).
From a purely historical perspective (overlooking his part in the crucifixion), Joseph Caiaphas was good at his job. This is known because he ruled for seventeen years without any major civil disturbance “during his watch.” That was “longer than any other high priest under Roman rule.” Making the feat more impressive, “for ten of those years Pilate was prefect.”
In spite of the fact that he was a Sadducee, Caiaphas would have sworn before a special court to uphold the most orthodox traditions surrounding the entry to the Holy of Holies. This was because the High Priest was the only person who could enter that sacred domain on Yom Kippur. Therefore, he swore “to ensure that the ceremony was carried out in strict accordance with tradition.”
Dispelling another popular myth, it is a fact that the Jews of ancient Israel were quite autonomous under Roman rule in the early part of the first century CE. This was due in part to the success of Jewish leadership. “Rome did not actually govern Judaea on a day-to-day basis.” The local citizenry may not have liked the High Priest, but they deeply respected the position. That level of respect and submission was the basis upon which the Romans chose to permit “self-rule” to the degree it was allowed. Rome saw it as the easiest method to control a remote, hostile, distant area of the empire. Without qualified and capable “native” leaders, ancient Israel would have required more cost to control the area than it was worth. Later, Rome realized their error. The Jews carried out a major revolt against the Roman Empire (66-70CE). Israel learned their lesson after Rome’s “scorched earth” policy was implemented during the second unsuccessful Jewish revolt (115-117).
Clothes Make the Man & Priest!
One control retained by Rome during the time of Jesus insured that Roman officials retained authority during the important time of Jewish festivals. The pilgrimage festivals were of particular concern to Roman leaders. It was at the time of these celebrations that pilgrims flooded Jerusalem to visit the Temple.
Jesus came from the countryside to the city for major festivals. In much the same way, tremendous crowds of Jewish worshippers entered the city at the appropriate times to visit the priests and make their sacrifices. The trump card needed to retain authority over the priests was controlling their vestments. By this they were sure to keep the loyalty of the leaders. The priest could not perform his duty without his priestly garments.
First Herod and then Rome took control of the high priest’s vestments and released them only on special occasions. With them on, he wielded too much authority. Cases concerning control of the vestments, and with it the appointment of the high priest, more than once went directly to the Roman emperor for decision. Who controlled the vestments and the office really mattered; it mattered because the man in the office was intermediary not only between Rome and the populace, but also between God and his people. He was the one who, on the Day of Atonement, went into the Holy of Holies, and who made atonement for the sins of the people of Israel. 
Kittel: A White Robe for Purity
Although different from the vestment of the priests, it is still customary for Jewish leaders (and other observant Jewish men) to wear distinct garb on the High Holidays. A special white robe known as a kittel is a traditional garment during the season. The white color represents purity which is what repentant believers seek through prayer and fasting. The reason for the kittel does not end with hope for a clean slate. It also represents the white burial shroud that is used at traditional funerals.
On Yom Kippur, we are meant to feel the touch of death, for death cuts through all the defenses and illusions we have carefully created around our own mortality. 
You see, the Hebrew Bible gave very specific instructions about the Temple requirements for the forgiveness of sins. Different sins called for different types of sacrifices. Within biblical Judaism, forgiveness did not exist apart from the prescribed biblical sacrifices.