Gregory the Great — on Judg 7:5-7 (Morals on the Book of Job, Book 30.74)

“And they are brought to the river, to drink the waters; and whoever drank the waters with bended knees, were removed from the struggle of war. For by the waters is designated the doctrine of wisdom, but by the unbended knee righteous conduct. They therefore who are reported to have bent their knees, while drinking the water, retired from the strife of battles, having been forbidden; because Christ proceeds to battle against the enemies of the faith, with those who when they drink the streams of doctrine, distort not the uprightness of their actions. For all are said at that time to have drunk the water, but not all to have stood with unbended knee. And they who bent their knees, while they were drinking the waters, were rejected, because, as the Apostle witnesses, "For not the hearers of the law are just before God, but the doers of the law will be justified." For since dissoluteness of conduct is, as we have said, signified by this very bending of the knees, it is rightly again said by Paul, "Lift up the hands that hang down, and the feeble knees, and make straight steps with your feet." They therefore proceed, under Christ as their leader, to battle, who exhibit in their conduct that which they profess with their mouths, who drink spiritually the streams of doctrine, and yet are not carnally distorted by wicked works.”