It was expected that kings would take sons and daughters to use in his service (1 Samuel 8:11–13). There are a number of reasons why Saul kept David at court. His close friendship with Jonathan may be one of the reasons.1 Alternatively, because of David’s fame and favour amongst the people, Saul wanted to make exclusive use of him.2
2 And Saul took him that day and would not let him return to his father’s house.