Unto the captain of their thousand; in whose power it was in a great measure, either to preserve them, or to expose them to utmost hazards. Take their pledge, i.e. bring me some token of their welfare from them.
Related Commentaries of 1 Samuel 17:18
1 Samuel 17:18
18 And carry these ten cheesesd unto the captain of their thousand, and look how thy brethren fare, and take their pledge.