Israel is the Jewish State, and Jewish holidays are part of the national calendar. In the Jewish calendar, each day begins at sunset and ends at sundown of the following day. So Shabbat (the Sabbath) begins at sunset on Friday, and ends 25 hours later at sundown on Saturday.
The Israeli weekend is Friday and Saturday; Sunday is a normal working day
The first and last days of Passover (Pesach), Shavuot (Pentecost), Rosh Hashana (New Year) (two days), Yom Kippur (Day of Atonement) and the first and last days of Sukkot (Tabernacles) are holidays with banks, businesses and offices closed.
Holidays such as Purim and Chanukah are celebrated throughout the country, but nothing is closed.
Israel’s Christians, Muslims, Druzes and Baha’is celebrate holidays on the appropriate days; Catholic and Protestant Christians celebrate Christmas and Easter according to the international calendar; Orthodox Christians celebrate these holidays about two weeks later.