If God is “one” — and that seems to be a pretty fundamental precept of Judaism — then why does God have so many different names? The standard answer is: because God has different "aspects" of His being, and each name emphasizes a different aspect. Our Sages tell us (in Bereishit Rabbah 33:3) that YHVH ("Hashem") describes God's attribute of mercy, whereas Elokim describes God's attribute of strict justice. Those are the two most common names of God that we encounter in the Torah.
But there are some other, less common names whose meaning seems more evasive. Like Kel Shakkai (literally translated as "El Shaddai," but the convention is to say and write "Kel Shakkai," out of respect for the holiness of God's name). The name Kel Shakkai only comes up a scant handful of times in the entire Torah. It is most mysterious indeed. And perhaps most mysterious of all, God opens up Parshat Va'era with the following comment to Moses: "I am YHVH. I appeared to Abraham, to Isaac, and to Jacob as Kel Shakkai, but with my name YHVH, I wasn't made known to them" (Exodus 6:2-3). What is the meaning of this? What is the "essence" of the name Kel Shakkai? Why did God reveal that name to our forefathers? Why did He conceal from them the name YHVH?
Watch Rabbi Fohrman's analysis of God's name Shakai: ''Finding God In Science''.
Read Beth Lesch's blog for a deeper discussion of the meaning of "God is my Shepherd".