The promises to David from 2 Samuel 7:4–17 are clearly in view in Psalm 2, especially in verses 5–12. In 1 Kings 2:1–4 and several other passages these promises are specifically applied to Solomon. These promises are also significant in the accounts of kings such as Hezekiah and Josiah. There is a sense, then, in which the promises apply to the line of kings that descends from David. This line culminates in Jesus, in whom the promises are ultimately fulfilled.
The problem with capitalizing son in Psalm 2:7 is that it cuts straight from from 2 Samuel 7 to Jesus. It’s great to get to Jesus, but the short cut keeps readers from seeing the typological development that grows and deepens through the accounts of the sons of David. This can keep us from understanding what Jesus meant when he declared that one greater than Solomon had arrived (cf. Matt 12:42).
So capitalizing son in Psalm 2:7 gets the termination point right, but it can keep us from feeling the buildup of the development that swells and plunges between David and Jesus.
Originally posted at BibleGateway