The pasuk in Yechezkel (16:6), which we read in the Haggada, repeats the phrase, "In your blood you shall live." The midrash (P’sikta 17) says it refers to the blood of mila and the blood of Korban Pesach. We are forbidden to give the Korban Pesach to a non-Jew or to one who does not have a brit mila (Shemot 12:43,48). Pirkei D’Rabbi Eliezer says: "In the merit of the blood of brit mila and Korban Pesach, they were liberated from Egypt, and in the merit of the blood of brit mila and Korban Pesach, they will be liberated at the end of ‘the fourth kingdom.’"
The Korban Pesach represents the liberation. We are to eat roasted lamb with the whole family celebrating as a unit at an elaborate meal, on the one hand, and eat matza and maror to remember the past, as well. Only if, at the time of success, we remember the times of affliction, can we be sure that the light of success will not blind us. This is best accomplished when there is first a brit mila.
There are many who are ready to sacrifice for independence as long as that independence seems fit for posh festivities. At that point, one does not want to have to remember the past with its difficulties. One wants to see in the independent nation a new nation, in our case, not the same "Yiddelach" from the exile. A certain self-pride is born, as we see, with a hollow boastfulness, which can eventually turn into empty disregard for others. To combat that, we need the blood of mila. The independence of Israel is a chain of self-sacrifice, whose purpose is not to let us rest on our laurels. Indeed, one who is not circumcised cannot take part in the full Pesach celebration. Without a life of purity, independence can be dangerous.
This is what Chazal (Shemot Rabba 3:4) meant in saying that Bnei Yisrael went down to Egypt with the word "anochi," were taken out with the word "anochi," and will be redeemed at the end of time with "anochi" ("Alas, I (anochi) am sending you Eliya the Prophet"). Some think that one can be liberated without calling out in the name of Hashem (anochi), as the other nations can. Without anochi the hearts of the fathers are not lined up with the hearts of the sons (see Malachi 3:24). This is not only in regard to Torah observance but when things are done wrong, the younger generation will be disillusioned with that which their fathers cherished and fought for. We already see the emergence of youth who feel over-entitlement. That is because one who does not keep on a straight line, will grow increasingly crooked.
For the liberation at the end of the fourth liberation there is a need for preparation done by Eliyahu before the "day of Hashem" and "the offering of Yehuda and Yerushalyim like the days of the past." The navi (ibid. 4) referred to it in a double language that hints about the time of Moshe and the time of Shlomo (Vayikra Rabba 7:4). Both before the time of the particular national emergence (time of Moshe) and before the time that will usher in an era where all of mankind will learn from the Torah emanating from Zion (time of Shlomo) there is a need for Eliyahu to set the stage.