One of the most important Scripture that reveals the OT use of Yahweh and Elohim, usually translated LORD and God in the KJV, is the following. Moses recorded what was spoken, but also adds various comments under inspiration, and it is important to note some of the unique expressions used.
Exodus 3:1 (KJV): 1 Now Moses kept the flock of Jethro his father in law, the priest of Midian: and he led the flock to the backside of the desert, and came to the mountain of God, even to Horeb. 2 And the angel of the LORD appeared unto him in a flame of fire out of the midst of a bush: and he looked, and, behold, the bush burned with fire, and the bush was not consumed. 3 And Moses said, I will now turn aside, and see this great sight, why the bush is not burnt. 4 And when the LORD saw that he turned aside to see, God called unto him out of the midst of the bush, and said, Moses, Moses. And he said, Here am I. 5 And he said, Draw not nigh hither: put off thy shoes from off thy feet, for the place whereon thou standest is holy ground. 6 Moreover he said, I am the God of thy father, the God of Abraham, the God of Isaac, and the God of Jacob. And Moses hid his face; for he was afraid to look upon God.
7 And the LORD said, I have surely seen the affliction of my people which are in Egypt, and have heard their cry by reason of their taskmasters; for I know their sorrows; 8 And I am come down to deliver them out of the hand of the Egyptians, and to bring them up out of that land unto a good land and a large, unto a land flowing with milk and honey; unto the place of the Canaanites, and the Hittites, and the Amorites, and the Perizzites, and the Hivites, and the Jebusites.
It is important to note that it was the Angel of Yahweh that appeared to Moses. It was not Yahweh Himself, and therefore it was not God in the English sense of the word. But note v4, it is Elohim that calls unto Moses out of the midst of the bush. This Angel also states “I am the Elohim of thy father, the Elohim of Abraham”. And Moses records that he was afraid to look upon Elohim. And then in v7 the Angel speaks as if he was Yahweh: “Yahweh said …I am come down to deliver them out of the hand of the Egyptians”. The conclusion that can be gathered from all of this is that the Angel represents God the Father, and speaks on His behalf, as if the Angel is God Himself, and both the Name of God, Yahweh and the title Elohim are directly used when describing the Angel.
When considered, as this is Moses’ first encounter with an Angel, and even though it appears in the Second Book of Moses, Exodus, it establishes the use of these unique Hebrew words and ideas, not only in the Books of Moses, but all of the OT. This is especially relevant with regard to the Angels in Genesis 1-3, Genesis 1:26-27, Psalm 8:5 and the Judges in Exodus 21:6 and elsewhere. It also helps to explain John 20:28.
Kind regards
Trevor