The Bnei Ephraim miscalculated that the enslavement was from bris bein habsorim and left 30 years earlier as indicated in the Targum Yonasan in the beginning of Parashas Beshalach. Hashem did not want the Bnei Yisrael to see 200,000 Bnei Ephraim’s dead corpses which were murdered by the Philistines because of leaving thirty years before the time and their dry bones were seen by Yechezkiel being revived in Bikas Dura. When seeing that, they would have returned back to Mitzraim. The GRA explains the naming of the 5th cup ??? ?? ????? as there is a doubt that maybe we should take five cups as the promise, ??????, to be brought to EY, no more in effect, should also be counted, so Eliyahu Hanavi will answer that.
