John Gill Commentary Psalms 132:17

"There will I make the horn of David to bud: I have ordained a lamp for mine anointed." — Psalms 132:17 (ASV)

There will I make the horn of David to bud
Which the Targum interprets "a glorious" King; and both Kimchi and Ben Melech, and also Arama, understand it of the Messiah, and very rightly; called the horn of the Lord's Anointed, and the horn of salvation, (1 Samuel 2:10) (Luke 1:69) ; expressive of his power and strength, in allusion to the horns of cattle, with which they push their enemies and defend themselves; so horns are interpreted kings, (Daniel 7:24) ; and is fitly applied to Christ, raised up of the seed of David, the man of God's right hand, made strong for himself, who is a mighty King and an able Saviour; as appears by what he has done and suffered, by the deliverance and salvation of his people, and by the destruction of all their enemies.

And it should be further observed that the Lord says, "there" will I do it; that is, either at Ephratah, which is Bethlehem, the place where the Messiah was to be born, and was born; or else at Zion or Jerusalem, where he appeared and showed himself, where he taught his doctrines and wrought many of his miracles, and near to which he suffered and died; and this shows that the Messiah must be come, that this horn of David must have budded, or the man the branch brought forth, since Bethlehem and Jerusalem are long ago demolished.

I have ordained a lamp for mine anointed ;
which Jerom understands of John the Baptist, the forerunner of Christ, who was a burning and shining light, but was not "that light", that famous light, that was to come, but was sent to bear witness of it; he being but as a candle, as the word here used signifies, in comparison of the sun of righteousness; but rather it means a son and successor of David, the Lord's anointed; in which sense the phrase is often used, (1 Kings 11:36) (15:4) (2 Kings 8:19) ; and here the famous and illustrious Son and successor of his, the Messiah, the light which enlightens every man with the light of reason; and who is the light of the world of his people, enlightening them with the light of grace, and will be the light of the New Jerusalem state, and of the ultimate glory; him God has "ordained" as such, even foreordained him before the foundation of the world; this lamp, or light, he prepared in eternity, and it dwelt with him, and therefore was desired to be sent out from him, (Daniel 2:22) (Psalms 43:3) ; which places are to be understood of the Messiah; (See Gill on Daniel 2:22) and (See Gill on Psalms 43:3).