At the beginning of Parashat Va'era, God says to Moshe: I appeared to Avraham, Yitzchak, and Yaacov as El Shaddai, but I did not make Myself known to them by My name Y-H-V-H (Exodus 6:2). Rashi explains that the early ancestors had a difference experience of God than the Israelites would in Egypt. The chassidic commentator Noam Elimelech, Rabbi Elimelech of Lizhensk, elaborates by comparing these two names of God to a mezuza on the doorpost.
Reb Elimelech notes that Shaddai is the name that appears on the case of the mezuza, facing out. This name represents an outer layer of the experience of God -- for instance, as the exercise of power. But inside the mezuza, enclosed, is a passage from the Torah and essential name of God, the letters Yod-Hay-Vov-Hay. This is the "heart", the living Torah and the living God.
From the beginning of the Torah, God is the Creator, and the patriarchs know God that way. Yet for some reason, they don't always turn toward God at times of trouble. God addresses them, and they respond. Only occasionally do they call out to God. Yitzchak and Rivka do, when they are childless and during her difficult pregnancy. But Yaakov -- Yisrael -- does not, through years of difficulty in many lands.
The Creator God -- the Almighty, Shaddai -- is not the aspect of God that speaks universally to the heart and draws it near. If creating the world isn’t enough to wow human beings, then God needed to find something else big enough, important enough, to be a message people would understand about God's true nature.
A great musician is proven by playing the most difficult or intricate repertoire. A great athlete is tested by the post-season, against the stiffest competition. So God can’t really be understood just by God's helping out one family, or bringing a season or two of prosperity to the land.
No, God will be understood by coming to the side of a nation in the time of its greatest suffering, its lowest demoralization, against the most powerful tyrant who calls himself a powerful God. The compassion that God shows now, and the power that God displays against oppression -- these are truly gadol, big and great, in the deepest way. Even bigger than creating the universe, which after all God did almost without any effort at all.
That’s why God’s name, God’s nature, comes to be known fully only now, in Egypt, for the slaves. If we want to know God completely, not just in the stars or in the beautiful designs around us, we will know it as compassion when compassion seems least likely. As strength on our side when there seems to be no strength, and as support when all the weight is on the other side. Building and making things -- even for human beings this is easy, and so too for God. These other things often seem impossible. Only the shadow of Egypt can make us truly appreciate the light that is God.