Who is this 'son of your body' God promises? It's a puzzle that points to a King far greater than any earthly monarch.
The core of God's oath to David is the guarantee of a successor. "One of the sons of your body I will set on your throne." This promise, first spoken in 2 Samuel 7, isn't just about Solomon who succeeded David. While Solomon was a fulfillment, the promise reaches far beyond him.
This points directly to Jesus Christ. He is the ultimate 'son of David' (according to the flesh) who sits on an eternal throne. God's promise was an assurance that David's lineage would continue and, ultimately, lead to the Messiah who would establish an everlasting kingdom. It secured David's dynasty and pointed towards a King who would rule with perfect righteousness.