The title in Hebrew occasionally means “master” (see Psalm 12:5 where it refers to the master of servants; see also Jeremiah 22:18; Jeremiah 34:5; Psalm 105:21). But in most cases by far, it refers to God, and appears in phrases such as “the Lord Yahweh,” or “the Lord of all the earth.” Here the reference is clearly to the Lord God. This fits with the context. The Jews were longing for the Lord to come in judgment.
1 “Behold, I send my messenger, and he will prepare the way before me. And the Lord whom you seek will suddenly come to his temple; and the messenger of the covenant in whom you delight, behold, he is coming, says the LORD of hosts.