The choice of the הפטרה for שבת הגדול is puzzling at best. After all, each of the previous special הפטרות were specially chosen to match the particular theme of that שבת and the special additional Torah reading. The הפטרה for פרשת שקלים refers to collections taken for the בית המקדש. The one for פרשת זכור recalls a prior battle with עמלק, the selection read on פרשת פרה discusses purification and for פרשת החודש we read about the special procedures used in the בית המקדש on ראש חודש ניסן. It is surprising, then, that שבת הגדול has no special Torah reading, and that the special הפטרה selected has no seeming connection to the day.
Quite a number of suggestions have been offered - the most famous of which refers to the penultimate פסוק of the הפטרה, one that is repeated after the conclusion of the הפטרה. That פסוק makes reference to the יום הגדול, hence the שבת is called שבת הגדול. This, of course, is an example of circular reasoning, for it explains the name of the שבת without actually explaining why this particular הפטרה was chosen for this week.
Truth be told, the content of this הפטרה is rather jarring, as the נביא describes depth of the חוצפה of the Jews and the guarantee of punishment for them. ה' offers a challenge to His people - a challenge to which they apparently fail to rise to meet. Even that famous פסוק of the יום הגדול והנורא is one that is pregnant with danger, especially when read in the context of the following one, which warns of impending desolation. Why, then, was this selection chosen for the שבת before פסח?
Perhaps, it could be suggested, that the selection of this הפטרה has less to do with its content than with its location in תנ"ך. The selection we read is from ספר מלאכי - to be more precise, the very end of מלאכי. מלאכי represents the end of revealed knowledge, the end of prophecy. One can only imagine the terror of בני ישראל suddenly realizing that they were cut off from direct Divine knowledge, particularly having just gone through חורבן בית המקדש and גלות בבל. Imagine the terror of an astronaut stuck in space being told that there will be no further transmissions from NASA, and that the astronaut will have to figure out for himself (based on earlier transmissions) how to get back to Earth. Over and over the astronaut will read and reread the final transmission, looking for some clue that will help him figure out the way home.
As we approach פסח, we cannot help but remember our first redemption, from מצרים. We spend the greater part of a month preparing to commemorate and relive the גאולה of years gone by. At the same time, we cannot avoid thinking about our current situation, and how desperate we are for a redemption from this exile - a redemption that, according to ירמיה הנביא will dazzle us with its brilliance so that גאולת מצרים pales in comparison. ..ולא יאמרו עוד חי ה' אשר העלה את בני ישראל מארץ מצרים כי אם חי ה' אשר העלה ואשר הביא את זרע בית ישראל מארץ צפונה (ירמיה כג:ז-ח). "People will no longer swear in the name of God who brought the Israelites out of the land of Egypt, will swear in the name of God Who brought the children of the Israelites out of the land of the north .."
The very memory of our first redemption evokes the hunger pangs for the ultimate redemption of the Jewish people - the one referred to at the close of ספר מלאכי, ה''s final message. And so, on the שבת before פסח, we grab on to the very last words ה' said to us, reading and rereading, looking desperately for some clue to help us find our way back. That final prophecy speaks of the יום הגדול והנורא - that awesome and fearful day, yet promises that on that day our offerings will be accepted as they were in the days of old. It is a prophecy we still struggle to understand, yet cling to till the end.