Midras 1 Samuel 17:45: Aggadat Bereshit, Mekhilta DeRabbi Yishmael, Midrash Tanchuma & Bamidbar Rabbah

Chapter 3: Writings [1] For an educated conductor, a song of David, when Doeg the Edomite came and told Saul, saying, “David has come to the house of Ahimelech.” (Psalm 52:1-2) This is what the scripture said: "You will be sheltered from the scourging and burning tongue." (Job 5:21). The language of evil is harder to retract than a sword or a knife, for how can one who has a sword in his hand and wants to kill his fellow man and then regrets it, retract his hand and not kill him? But one who seeks to kill his fellow man with an arrow cannot retract it once it has left his hand. And one who speaks evil about his fellow man, even if he wants to retract it, cannot do so. Why? Just as the arrow is likened to the language of evil, as it says, "Their tongue is a sharpened arrow, deceitful speech in their mouth, etc." (Jeremiah 9:7), so too, King Solomon says, "All of man’s earning is for the sake of his mouth, etc." (Ecclesiastes 6:7), even if he dies, there is no atonement for him. Come and learn from Doeg, who even though he died, our sages said he has no share in the world to come, as it says, "But the soul that sins, it shall die" (Ezekiel 18:20). Therefore, Job said, "The language of concealment is in my mouth." Rabbi Yehoshua ben Levi said it refers to Jacob, and Rabbi Samuel bar Nachmani said it refers to David. "You will redeem my soul in peace from the battle that is upon me" (Psalm 55:19). When he fled and came to Ahimelech and was hungry, and he ate the holy bread, as it says, "And the priest gave him the holy bread, etc." (1 Samuel 21:7). "and in war by the hand of the sword." (Job 5:20). When he went down to Goliath and killed him, as it says, "And David said to the Philistine, 'You come to me with a sword, etc.'" (1 Samuel 17:45). "In a smooth tongue you will hide, when Doeg came and spoke evil about him, as it is said about Doeg the Edomite, 'and he told'." (Psalm 52:2) "You shall laugh at destruction and famine" (Job 5:22). i will take care of Ahithophel, "And have no fear of wild beasts." (Job 5:22). Saul of Benjamin is compared to a predator, as it is said, 'Benjamin is a ravenous wolf' (Genesis 49:27)."

And thus did David say to Goliath (I Samuel 17:45) "You come to me with a sword, a spear, and a javelin — but I come to you with the name of the L–rd of hosts, the G–d of Israel." And it is written (Psalms 20:8-10) "These with chariots and these with horses; but we, in the name of the L–rd our G–d will call. They knelt and they fell, but we rose and gained courage. O L–rd, save! The King will answer us on the day that we call."

"the L–rd is His name": It is with His name that He wars, and He has no need of any of these (military) appurtenances. And thus did David say (I Samuel 17:95) "You come to me with sword, and spear, and javelin; but I come to you with the name of the L–rd of hosts, etc." And (Psalms 20:8) "These with chariots and these with horse, but we with the name of the L–rd our G–d, etc." And thus did Assa say, viz. (II Chronicles 14:10) "And Assa called out to the L–rd his G–d and said: O L–rd, there is none besides You, etc."