The Sabbath before Passover is called Shabbat HaGadol (שבת הגדול), which loosely translates to “The Great Sabbath.” Why is it called the Great Sabbath? Jewish tradition has forgotten the origin of the name.
The sages and rabbis made several suggestions to explain the name. It may reflect the influx of pilgrims into Second Temple-era Jerusalem during the week before Passover. One tradition says that on the Sabbath before the original Passover in Egypt, the Egyptians tried to stop the Israelites from preparing lambs for sacrifice, but the LORD miraculously intervened. Because of the miracles that God performed on that day, the Sabbath before Passover became known as “the Great Sabbath.” Other traditions associate the name with the lengthy sermons and teachings about Passover that the rabbis present on the Sabbath before festival.
The most likely suggestion derives the name from the haftarah portion—the synagogue reading from the prophets. The haftarah portion for the Sabbath before Passover predicts the coming “great and terrible day of the LORD” (Malachi 3:23[4:5]). The Sabbath on which this passage is read may have derived its name from it.
Judaism considers the Festivals of Passover and Unleavened Bread as the prototype for the final redemption. The tradition of setting a place at the seder table for Elijah the prophet reflects the ardent belief that Messiah will bring redemption at Passover. As the anticipated herald of the Messiah, Elijah will need to be present as the festival begins. For the same reason, the sages chose Malachi 3:4-3:24 (4:6) as the haftarah portion for the Sabbath before Passover. Since this passage of Malachi predicts the coming of Elijah before the day of the LORD, it makes an appropriate introduction to the prophetic anticipation of the Passover season.
The haftarah begins with the announcement that God will one day favorably receive the sacrificial services as he did in ancient times. Before that happens, though, a time of judgment must purge the people and priesthood. The LORD will bring correction to the people’s moral apathy. Their apathy results from their disbelief in God’s just providence. In the day of the LORD, when God punishes sinners and rewards the righteous, everyone will see that God is just. Before that day, the LORD will send Elijah the prophet to return his people to the Torah of Moses and to reconcile fathers and sons:
Behold, I am going to send you Elijah the prophet before the coming of the great and terrible day of the LORD. (Malachi 3:23[4:5])
According to Jewish tradition, Elijah did not die—he is in heaven, anxiously awaiting the redemption. Before the arrival of Messiah, the Prophet Elijah will appear. This is why “the scribes say that Elijah must come first” (Matthew 17:10). According to our Master, however, “John the Immerser himself is Elijah who was to come” (Matthew 11:14). John came “as a forerunner before [Messiah] in the spirit and power of Elijah” (Luke 1:17).
He will restore the hearts of the fathers to their children and the hearts of the children to their fathers, so that I will not come and smite the land with a curse. (Malachi 3:24[4:6])
What does it mean that Elijah will restore the hearts of the fathers to their children and vice versa? The word “restore” is a translation of the Hebrew word for return and repent. Elijah’s mission will be one of turning hearts to repentance. The oracle of Zechariah the priest predicted that John the Immerser would “turn the hearts of the fathers back to the children, and the disobedient to the attitude of the righteous, so as to make ready a people prepared for the Lord” (Luke 1:17).
Source: First Fruits of Zion