John Gill Commentary 1 Samuel 18:2

"And Saul took him that day, and would let him go no more home to his father`s house." — 1 Samuel 18:2 (ASV)

And Saul took him that day
Not only into his favor, and into his service, but into his court; even on that very day he slew the Philistine, or however as soon as it could be done:

and would let him go no more home to his father's house ;
as he used to do before; when he only served as a musician to him, then he was only at court when Saul was in a melancholy disposition, and wanted him, and so was going and returning, and in the intervals kept his father's sheep, (1 Samuel 17:15) ; but now he would not suffer him to attend such business any longer, since he was not only to become a courtier, and be made a prince or noble, but to marry his daughter, according to the declaration he had made, with respect to any man that should kill Goliath.