Halakha Mazmur 132:12: Mishneh Torah, Kings and Wars

The king is anointed with the (original) Anointing Oil⁴Prepared by Moses., as it says, “Then Samuel took the vial of oil and poured it upon his head, and he kissed him” (I Samuel 10:1). The anointing qualifies him and his sons in perpetuity, and ensures that the monarchy will be hereditary, as it says, “In order that he may have many days in his reign, he and his sons, among Israel” (Deut. 17:20). If the king (dies and) leaves a young son, the monarchy is retained for him until he gets older, as Yehoyadah did with Yoash. Those who take precedence in (the laws of) inheritance, take precedence for succession to the throne; and the older son precedes the younger one. This is not only true for the monarchy but for all governing Positions and all appointments in Israel – a son inherits from his father, and so his son from him, forever. This is as long as the son follows in his father’s footsteps with regard to wisdom and awe. If the son was G-d-fearing but lacked wisdom, he is appointed to succeed his father, and trained. However, if he was not G-d-fearing, even though he was very wise, he is not appointed to a Position in Israel. From the time David was anointed he merited the crown of kingship, the monarchy became his and that of his male descendents for all time, as it says, “Your throne, will be established forever” (II Samuel 7:16). This only refers to those who are of legitimate lineage, as it says, “If your sons shall observe my covenant” (Psalms 132:12). Even thought he only merited the monarchy for his descendents who have legitimate lineage, the monarchy will never be withdrawn from the descendants of David. The Holy One, Blessed Be He, had promised him as such, as it says, “If his children forsake my Torah and walk not in My statutes,…and I shall visit their transgression with the rod, and their iniquity with disease. But My mercy I shall not break off from him” (Psalms 89:31-34).