1 Samuel 17:36,37

Thy servant slew both the lion and the bear, &c. There is a remarkable, and never to be sufficiently admired modesty in this relation of David, which he concludes by attributing all he had done to the goodness and power of God. And he takes encouragement from the experience which he had already had of these divine attributes being exerted on his behalf on a less important occasion, to believe that they would be exerted on this occasion also, which was much more important, as peculiarly involving the glory of God and the best interests of his people, which had not been the case in the former instances. This uncircumcised Philistine shall be as one of them Goliath debased himself below a brute by his blasphemy, and therefore he now carried no more terror with him to David than a lion or a bear. Seeing he hath defied the armies of the living God Here we see the foundation of David's confidence of success. The Philistine had defied the living God in defying his armies, and had openly avowed himself his enemy. And David therefore comes forward, as his friend, to espouse his cause. It is as if he had said, The lion and the bear were only enemies to me and to my sheep, and it was only in defence of them that I attacked these brute beasts; but this Philistine is an enemy to God and his people, and it is for their honour that I attack him.