The first problem many if not most interpreters have--and here, I point to such a paradigmatic text as Ps.8:4; and suggest that men should have begun their study here, until they had found what Carson identifies as a coherent hermeneutic, before running off to teach others--they do not let the NT explain the OT. Nor do they listen to the OT as the pedagogue it is.
What is man, that you are mindful of him,
And the son of man that you visit him?
You have made him a little lower than the angels,
And you have crowned him with glory and honor.
A very basic question is: what does v4 say on its own terms? Is the parallelism
strict, or (as is often the case) is it
synthetic. It is the latter, and the term "son of man" is not just another poetic reference to the human nature, or man-in-general.
The "son" bore a special relation to the "father," and especially with regard to kingship and sovereignty. The son was the image of the father, and his primary representative. The king of some people was the current successor to his ultimate father, the founder of that people. The king was the "son," until he had a son of his own and that son succeeded him; then in death the king became most fully one with his own fathers. Meanwhile, his own son (while the father still lived) was in his faithful representation the best ambassador of his father; and revered his father even after he ascended the throne of his father.
Ps.2 is a "coronation" psalm; it is the day the son is publicly recognized as his father's true image and successor. v7 uses "son" in this way. This Psalm is ultimately not about David's son proper, or grandsons (etc.) but about the Christ, with God (being Israel's true King) is the Person actively acknowledging his successor--succession that in earthly terms was first celebrated when the earthly king's son was made co-regent under his father. His entering later upon a solo-reign when his earthly father died was an echo of his prior instatement.
"Son of man," (8:4) in its highest sense, is "covenant-man," the federal or great representative man. Thus, v4, reflecting on the wonder that God has condescended to man, asks (rhetorically), "What is a [mere] man, that you O infinitely great God regards man at all,/ Or who is even
the greatest representative of our race (or nation, esp. the covenant-nation) that you attend to him?" v5 says, "You have made him a little lower than the angels...," which speaks of human glory as naturally just beneath the glory of angels. The writer of Hebrews closes his opening section (chs 1&2) by using this text to teach that the Christ was first seen lower than angels, but then exalted to ultimate honor, and "all things," v6, is expanded beyond earthly creation to include the angels also.
The king of Israel was the highest man in the nation, and God's representative son. Israel being the chief of nations (alone in special covenant with God) a "kingdom of priests," Ex.19:6, the king or son of Israel was also a "son of man," a great representative of mankind. Among other kings, one might recognize all of them as equals of a sort, all are "sons of man;" but still Israel's king was first among equals, he was THE son of man. And, as Ps.2:7 states so plainly, he is also the son (ultimately, Son) of God.
No angel is identified as God's "son," according to Scripture--a fact noted by the author of Hebrews. The mere man, even the highest man of all men, can only be called "son" in a limited sense. What would it take, therefore, for some man to be a peerless son-of-God? It would take a man with some other nature, really, a genuinely divine nature, not just an honorific.
Heb.5:5 takes the idea of sonship in Ps.2, and ties it to Ps.110 (which is as plain an assertion of the unity of the Psalter as any), and to the idea of a priest-king. Only by an ideal fusion of the son-of-God concept, and son-of-man concept, is it possible in Israelite religion for the throne to be united to the altar in a single person. The image of God (the king, associated with Judah), and the image of man (the priest, associated with Levi); through as David perceived a unique priesthood underived from genetics.
Indeed, God hinted at such even as he rebuked Eli, 1Sam.2:35 (see
http://equip.sbts.edu/wp-content/uploads/2018/10/SBJT-22.2-Jesus-as-Priest-N.-Perrin.pdf, p.83; HT Triablogue); cf. 1Sam.13:14; 2Sam.7:11. Someone who will "do what is in my heart and my mind" is surely a most beloved son. The only lingering question, respecting Ps.2:7, is "who might potentially take this royal designation beyond the (apparent) limits of a typical son of David?" Or to ask the same question slightly differently, who will be a priest for mankind in the place of Adam?
In Acts 13:33, Ps.2:7 is used in exactly the way Paul uses "declaratory" language in Rom.1:3-4. It is the resurrection from the dead that proves beyond all possibility of doubt that Jesus is the perfectly obedient Son, faithful unto death, and vindicated by the power of an endless life. Ps.2:7 goes from being a a mere earthly coronation hymn sung for a type of David's Lord-to-come, at the public proclamation of the heir-apparent in Jerusalem; to being a signal of Christ's resurrection and ascension, where the whole universe is called to attention as the Son is settled on the throne of David, raised to the pitch of exaltation.
The NT is saying:
this is it. No, there is no return by the Christ to a more diminished, raised not-so-high throne over in physical Jerusalem. Ps.2 was always about something greater than the type. It witnessed the type, but it anthemed the Antitype.
