Jerusalem is important to the Jewish people because it is Ir Ha-Kodesh (the Holy City), the Biblical Zion, the City of David, the site of Salomon's Temple, and the eternal capital of the Israelite nation.
Jerusalem is important to Christians because it is where the young Jesus impressed the sages at the Jewish Temple, where he spent the last days of his ministry, and where the Last Supper, the Crucifixion and the Resurrection took place.
Jerusalem is important to Muslims because it is where the prophet Muhammad ascended to heaven. After the holy sites of Mecca and Medina, Jerusalem is the third most sacred place of Islam.
Church of the Holy Sepulchre, also called the Church of the Resurrection by Eastern Christians.