There are broadly three categories of Jewish holiday: biblical holidays, those mentioned in the Torah (sometimes called the Jewish Bible); historic holidays, those that were celebrated in biblical times but are not mentioned in the Bible; and later holidays, those rooted in the twentieth century.
The holiday dates follow the Jewish calendar, which is based on both the solar and the lunar year. The structure of the calendar was formulated in the eleventh century of the current Western (Christian) era, a time when calculations for the length of the lunar year were quite accurate. Because many Jewish holidays have more than one significance, and are often connected to farming and harvest time, it was necessary to adjust the calendar so that holidays were celebrated in the right season. If the calendar were not adjusted to account for the fact that the lunar year is 10–11 days shorter than the solar year, then eventually the calendar would get out of sync and harvest time would have to be celebrated at the time of planting. To avoid this, Judaism adds a leap month to its calendar every two or three years to keep it in step with the solar year. The system is so accurate that an extra leap month must be added every 300 or so years. This explains why Jewish holidays move around in relation to the Western calendar. The Jewish day begins at sunset, which is why the Sabbath, for instance, is marked from Friday evening to Saturday evening.
Jewish holidays are celebrated in two ways: with a service of worship, and at home with the family. Daily prayer is a mitzvah or religious command for Jewish people. Jewish services of worship became more common in Judaism during the Babylonian captivity that followed the destruction of the First Temple some 2,500 years ago.The religious laws of the halakha allow sacrifice to God only in the Temple. To replace sacrifice, a culture of holding a service of worship evolved, a culture that thrived even after the Israelites returned to Judea.
On weekdays, in Judaism, three services of daily worship are held and during festivals there are often four. It is generally agreed that community prayer is more significant than private prayer. The weekday prayers of Judaism are the evening prayer of maariv, the morning service of shacharit and the afternoon service or mincha. There is an additional prayer or service on the Sabbath and other holidays, called musaf.
For religious services in the home, the family first states why the holiday is being marked, then they celebrate it together. This is often done at mealtimes, although the meal simply provides the setting. As they have been throughout history, togetherness and community are important in modern Judaism. A festive meal, seudat, takes two to three hours and begins with the blessing of wine and bread. Orthodox Jews, among whom the Jews in Finland are numbered, say these blessings in Hebrew, as they do all prayers. The blessing of the wine and the bread is followed by special blessings related to the holiday being celebrated. The foods served at a seudatvary in different parts of the world. In Finland, the foods are traditionally of Eastern European origin.