The evening service of Yom Kippur is named after this declaration
For many Jews, the essence of the Yom Kippur service takes place at the very beginning of the holiday, at the evening service that ushers in Yom Kippur. It is called Kol Nidre, the name derived from the first major piece of the Yom Kippur prayers, dramatically chanted at the evening service. All the Torahs are taken out, the entire congregation stands, and the cantor chants this formula three times. While most people think that Kol Nidre is a prayer, it is actually a legal formula, as described in this article. Reprinted with permission from The Jewish Religion: A Companion, published by Oxford University Press.
'All vows,' the opening words of the declaration, largely in Aramaic, at the beginning of the evening service on Yom Kippur in which all vows that will be uttered in the coming year are declared null and void. The declaration applies only to religious vows and has no effect on oaths taken in a court of law. If a person makes a vow, say, to deny himself wine for a certain period, perhaps as a, penance, he must keep his promise, which is thought of as a promise to God. But this applies only if the vow is uttered with full intent. A person's declaration beforehand that all vows he will take in the year ahead are null and void means that any vow he will make is held to be without sufficient intention and hence without binding power.
Because it was falsely assumed that Kol Nidre does apply to oaths taken in the court, Jews were suspected of unreliability in this matter and in a number of countries the infamous More Judaica, a special humiliating form of oath, was introduced when a Jew had to swear in court. Zechariah Frankel and others in 19th‑century Germany exposed the falsehood and explained the true meaning of Kol Nidre.
In the Middle Ages a number of rabbinic authorities were opposed to the Kol Nidre on the grounds that its effectiveness to nullify vows was very questionable. Yet the Kol Nidre is still recited in the majority of congregations, the night of Yom Kippur being referred to as 'Kol Nidre Night.' There is no doubt that it is the famous traditional melody, with its note of remorse, contrition, hope, and triumph, that has saved the Kol Nidre. The usual practice is for the reader to chant the formula three times, raising his voice each time. An interpretation given to the Kol Nidre is that the congregation declares, by implication, at the beginning of Yom Kippur: "See, O Lord, what miserable sinners we are. We make promises to live better lives each year and yet always fall far short of keeping them. Therefore, help us, O Lord, and pardon us for our shortcomings."