The Frierdike Rebbe said one time he saw the Rebbe Rashab break the Afikoman into 5 pieces. He originally thought that it just happened to break into five pieces, until one time he saw the Rebbe Rashab break it into 6 pieces and he put one on the side. The Frierdike Rebbe then asked what the reason for this was. The Rebbe Rashab answered that he will know when he gets older.
The Frierdike Rebbe was bothered not knowing the answer. The next day when they were walking to together, the Frierdike Rebbe sighed. The Rebbe Rashab understood that it was because he did not get to hear the answer to his question. He asked, “it matters so much to you?” and then proceeded to tell him the reason;
The middle Matzah corresponds to Yitzchok – יצחק. This is why יחץ contains the letters of יצחק. Afikoman (אפיקומן) represents Avraham, because it's made of the words אפיקו מן which means to give food, like Avraham who would feed everyone.
Yitzchok is the attribute of Gevurah, which is a great light, but its nature is to go up (like fire always by nature goes upwards). Since we need to bring this level down into vessels, we need to break the middle Matzah, to break the Gevuros of Yitzchok. The breaking is into 5 pieces is because there are 5 aspects of Gevurah. We do this with the Afikoman to “sweeten” the 5 Gevuros with the Chesed of Avraham – the nature of Chessed is to come down.
~ First night Seder 5698
