John Gill Commentary 1 Kings 11:36

"And unto his son will I give one tribe, that David my servant may have a lamp alway before me in Jerusalem, the city which I have chosen me to put my name there." — 1 Kings 11:36 (ASV)

And to his son I will give one tribe
Judah and Benjamin reckoned as one; (See Gill on 1 Kings 11:13), that David my servant may have a light always before me in Jerusalem, the city which I have chosen me to put my name there; or a kingdom, as the Targum; or an illustrious prince, a successor, shining in royal majesty and glory, to guide and direct, cheer and comfort, the people of Israel; be an honour to David's family, and a means of continuing the pure worship of God in the temple at Jerusalem; see (2 Samuel 21:17) (Psalms 132:17) .