In Mosiah 18:18 it says that Alma had "authority from God." According to McConkie and Millet, the reference here is to the priesthood which Alma held (see Mosiah 23:16; Alma 5:3). Exactly when or where he was ordained is not given in the Book of Mormon. It may be that his office of high priest in King Noah's court (see Mosiah 11:4,11; 12:17,25) was an actual priesthood office, an office to which he had been formally ordained by one having proper authority, this in spite of the abominations of the day. Second, it is not inconceivable that Alma could have been ordained by Abinadi. A third possibility is that heavenly messengers could have been sent to ordain Alma if circumstances precluded his having contact with some mortal holding proper authority. [Joseph F. McConkie and Robert L. Millet, Doctrinal Commentary on the Book of Mormon, Vol. II, p. 260]