SHABBAT HA-GADOL (Heb. שַבַּת הַגָּדוֹל; "the great Sabbath"), Sabbath preceding *Passover. The name ha-Gadol ("the great") derives, according to some opinions, from the declaration in the haftarah (Mal. 3:4,24) "Behold, I will send you Elijah the prophet before the coming of the great and terrible day of the Lord" (ibid., 3:23). This haftarah was selected in accordance with the popular belief that the messianic redemption of Israel will occur in the same month as its deliverance from the Egyptian bondage (rh 11a). Another opinion on the institution of the "great Sabbath" before Passover is that it was influenced by the Christian concept of the Saturday before Easter. In some ancient rabbinic sources the Sabbaths preceding Passover, Shavuot and Sukkot were also called Shabbat ha-Gadol (Elbogen, Gottesdienst, 551). On this Sabbath it is customary to read the greater part of the Passover *Haggadah during the afternoon service. In traditional synagogues, the rabbi delivers a sermon devoted almost exclusively to the rites and the *dietary laws pertaining to Passover.
Eisenstein, Dinim, 401–2.
"Shabbat Ha-Gadol." Encyclopaedia Judaica. . Encyclopedia.com. (January 21, 2019). https://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/shabbat-ha-gadol
"Shabbat Ha-Gadol." Encyclopaedia Judaica. . Retrieved January 21, 2019 from Encyclopedia.com: https://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/shabbat-ha-gadol