3 Nephi 3:19

Now it was the custom among all the Nephites, to appoint for their Chief Captains, save it were in their times of wickedness, some one that had the spirit of revelation, and also of prophecy; therefore this Gidgiddoni was a great prophet among them, and also was the Chief Judge.

It was the custom among all the Nephites to choose their chief captains from men who had the Spirit to speak God’s messages and tell about the future. They only did this differently when they were wicked. So this Gidgiddoni was a great speaker of God’s messages among them. He was also the chief judge.

The Nephites had a tradition—except during times of wickedness—of appointing military leaders who had the spirit of revelation and prophecy. Gidgiddoni was a great prophet among them, and also served as chief judge.