Here in the first line of this psalm, God reveals Himself in two ways. (1) The first one is L-o-r-d. Adonai in Hebrew. It is roughly equivalent to the English word, owner. So He introduces Himself, in this psalm, as the owner of the heaven and the earth. And then (2) we have L-O-R-D. This is the very famous Yahweh - the YHWH. The one that is translated there in Exodus as I AM that I am. It is interesting to put the emphasis in different places. I am THAT I am. (Just to play with that, once in a while, is kind of interesting.) The I AM - YHWH. He is the one who has made a covenant - an agreement - with man. He is the Eternal One.
YHWH is connected to other nouns, in order to further describe His character to you and me. We have Yhwh-nissi, which means God, my banner. That appears in Exodus 17:15. It is intended to give encouragement. And it will appear in places where God is teaching that we need to be encouraged, by the context of what He is teaching us in that area.
