They helped David against the band of raiders, for they were all mighty men of valor and were commanders in the army.
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
All these men of war that could keep rank,.... Well disciplined men: came with a perfect heart to Hebron to make David king over Israel; they were all of one mind, and quite hearty and sincere in fixing David on the throne of all Israel: and all the rest also of Israel were of one heart also to make David king; those who came not...
they helped David against the band--that is, the Amalekites who had pillaged Ziklag in David's absence. This military expedition was made by all his men (Sa1 30:9), who, as David's early helpers, are specially distinguished from those who are mentioned in the latter portion of the chapter.