There will I make the horn of David to bud. The "horn of David" budded most gloriously when "a rod came forth out of the stem of Jesse, and a branch grew out of his roots, and the Spirit of the Lord rested upon him" (Isaiah 11:1, Isaiah 11:2)—in other words, when Messiah appeared, and re-established the Davidian kingdom, which thenceforth has endured, and will endure for ever.
I have ordained a lamp for mine anointed. The metaphor is changed; but the idea is the same. Christ's coming shed a glory on David's house, and on the temple, and on David himself, such as had never previously illumined them.
David is often promised "a lamp" (1 Kings 11:36; 1 Kings 15:4; 2 Kings 8:19; 2 Chronicles 21:7). In Christ the lamp was given.