This is to distinguish the personal covenant name, translated as Lord,
from the more general word meaning master/lord.
In the Baal Epic, the Canaanite god Baal is also referred to as Lord of all the earth.
By using this phrase, it seems as if the Bible wanted to make it clear to us that the Lord and not Baal is truly the living God who rules over all the earth.
The Lord is no local despot but the world’s only sovereign. His dominion over the whole earth means that he owns everything in it and thus has the authority to distribute any particular piece—Canaan in this case—as he wishes.1
11 Behold, the ark of the covenant of the Lord of all the earth is passing over before you into the Jordan.