Bede : And David said to him: Can you lead me to this band? etc. David is advised to find and conquer the robbers, who is left sick by the Amalekites; because there are those who, having lived among heretics, by the laziness of their mind, do not have the strength to harm the good, and the same ones, suddenly favored and touched by divine grace, acquire sufficient strength from God to resist the perverse; indeed, it is much more convenient and certain through those who know the secrets of the heretics, being converted to the Catholic, their errant sayings are confounded. But what he asks to be sworn to him, that he will not be killed, and that he will not be handed over to his master, so that he will reveal to them the hostile band of persecutors; this surely he asks from his spiritual teachers, that only on this condition will he disclose to them the secrets of the heretics, if they show him without any doubt the faith by which he may escape perpetual death; nor allow him to be subjected again to vain doctrines. — Commentary on Samuel