1. The Translation of the Name This combination is also translated in two different ways. The first way is Lord Jehovah, such as in the ASV. The term Lord has only the first letter capitalized showing that the Hebrew word behind it is Adonai. The word Jehovah reflects the name YHVH. In other translations, such as the KJV, the translation is Lord GOD. The word Adonai, but the word GOD is in all capital letters to show that, in the Hebrew text, the word behind GOD is the name YHVH, not Elohim. Examples of this compound name are: Genesis 15:2; II Samuel 7:1820; Isaiah 7:7; and Jeremiah 1:6.
2. The Emphasis of the Name
What is the emphasis when these two primary names are used together? Referring back to the name Adon or Adonai, the emphasis there was that of a master, owner, or lord. So the first name still emphasizes God as the One who is in control of His universe and of His creation. The name YHVH emphasizes God as the Covenant Keeper. When these two primary names are compounded together, they emphasize God as the One who has the power and the strength to fulfill the covenants that He has made because He has total control of everything. While YHVH emphasizes God as the Covenant Keeper, that may only emphasize the concept of intention: to fulfill His covenants. If He did not have the power of control to fulfill His Word, then the best intentions would have very little practical value. The two names together emphasize the fact that God is the Covenant Keeper, and the reason He is able to fulfill His covenants is because He has the power and the strength and the control of His creation to bring these covenants to their ultimate fulfillment.
A good example of this concept in action is found in Exodus 2:23-25, where God promises to do something on the basis of the Abrahamic Covenant: And it came to pass in the course of those many days, that the king of Egypt died: and the children of Israel sighed by reason of the bondage, and they cried, and their cry came up unto God by reason of the bondage. And God heard their groaning, and God remembered his covenant with Abraham, with Isaac, and with Jacob. And God saw the children of Israel, and God took knowledge of them.
Here is the very clear concept that God is the Covenant-Keeper and, at this point, He intended to fulfill His covenant. The term YHVH emphasizes Him as the One about to keep His covenant; the word Adonai emphasizes His power to do so.
In Exodus 3:6-8, God said to Moses: Moreover he said, I am the God of your 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. And Jehovah said, I have surely seen the affliction of my people that are in Egypt, and have heard their cry by reason of their taskmasters; for I know their sorrows; 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 Canaanite, and the Hittite, and the Amorite, and the Perizzite, and the Hivite, and the Jebusite.
The uniqueness of this compound primary name Adonai YHVH emphasizes Him both the Covenant-Keeper and as the One who has the great power to fulfill these covenants.
Source: The Names of God: Page 9-10