On page 384 of his Jewish Publication Society commentary on Numbers, Jacob Milgrom distinguishes between Mari prophecy and the prophecy in the Hebrew Bible:
"At Mari the prophet delivers the divine message only to the king never to the people. The message, moreover, is devoid of social or ethical demands."
I read this last night, and it overlapped with my reading today. Today, I read Rolf Jacobsen's Many Are Saying: The Function of Direct Discourse in the Hebrew Psalter. (My write-up on this book will appear on this blog later this month.) Jacobsen distinguished between royal Psalms in the Hebrew Bible, and royal songs or oracles elsewhere in the ancient Near East.
According to Jacobsen (on page 93), ancient Near Eastern royal oracles were directed towards a specific sovereign, within a specific context. Jacobsen refers to an Assyrian document in which Sennacherib asks the gods Shamash and Adad by divination if a particular person was the heir to his throne, and they respond in the affirmative. The biblical royal Psalms, by contrast, are about kings in general from the Davidic dynasty (though Jacobsen says on page 6 that David was the original audience for many of them---or Jacobsen may mean that the texts wants us to believe that). The biblical royal Psalms are about God's faithfulness to the Davidic dynasty---which transcends any specific situation.
On page 95, Jacobsen refers to an Assyrian parallel with Psalm 2. In this parallel, the kings of countries conspire against the Assyrian king Ashurbanipal, and the goddess Ninlil---who calls herself Ashurbanipal's mother---resolves to defeat these countries and subordinate them to Assyria. Similarly, Psalm 2 talks about kings conspiring against the king of Israel, God defeating them, and God being the father of the king of Israel. But the Assyrian oracle was an assurance to Ashurbanipal alone, and there is no reference to a public gathering. Psalm 2, by contrast, was probably for a public gathering, such as the king's enthronement, according to Jacobsen (pages 95, 105). In Israel, the word of the LORD was made into Scripture, to be used by subsequent generations. But that does not appear to be the case for royal oracles in Assyria.