C. F. Keil and Franz Delitzsch on 1 Samuel 22:2

1Sa 22:2

There a large number of malcontents gathered together round David, viz., all who were in distress, and all who had creditors, and all who were embittered in spirit (bitter of soul), i.e., people who were dissatisfied with the general state of affairs or with the government of Saul, - about four hundred men, whose leader he became. David must in all probability have stayed there a considerable time. The number of those who went over to him soon amounted to six hundred men (1Sa 23:13), who were for the most part brave and reckless, and who ripened into heroic men under the command of David during his long flight. A list of the bravest of them is given in 1 Chron 12, with which compare 2Sa 23:13. and 1Ch 11:15.