There appears to have been an interval of some months between the preceding events and this renewal of the promise to Moses. The oppression in the meantime was not merely driving the people to desperation, but preparing them by severe labor, varied by hasty wanderings in search of stubble, for the exertions and privations of the wilderness. Hence, the formal and solemn character of the announcements in the whole chapter.
I am the Lord ... - The meaning seems to be this: “I am Jehovah (Yahweh), and I appeared to Abraham, Isaac, and Jacob as El Shaddai, but as to my name Jehovah, I was not made known to them.” In other words, the full import of that name was not disclosed to them. See Exodus 3:14.
God Almighty - Rather, “El Shaddai,” (שׁדי אל 'êl shadday), it is better to keep this as a proper name.