Some Gadites defected to David at his stronghold in the wilderness. They were mighty men of valor, trained for battle, experts with the shield and spear, whose faces were like the faces of lions and who were as swift as gazelles on the mountains:
We have here an account of those that appeared and acted as David's friends, upon the death of Saul, to bring about the revolution. All the forces he had, while he was persecuted, was but 600 men, who served for his guards; but, when the time had come that he must begin to act offensively, Providence brought in more to his assistance.
Commenting on 1 Chronicles 12:1-22
These are they that went over Jordan in the first month,.... The month Nisan or Ab; as they must come over Jordan to come to David, since they dwelt on the other side of it: when it had overflown all its banks; as it did at this time of the year, see Jos 3:15 which is observed to show both the time of the year...
of the Gadites there separated themselves unto David--that is, from the service of Saul and from the rest of the Gadites who remained steadfast adherents of his cause. into the hold--or fortress, that is, of Ziklag, which was in the wilderness of Judah.