"To the choirmaster of David, when Doeg the Edomite came and told Saul, "David has come to the house of Ahimelech." It is said in Ecclesiastes 5:5, "Do not be rash with your mouth, nor let your heart be hasty to utter a word before God." Rabbi Yehoshua ben Levi said concerning the verse, "Do not give your mouth to sin against your flesh" (ibid.), that the Scripture is speaking about those who rule on matters of charity.
"Do not give your mouth to flatter when you are giving, lest you give in stinginess and not in generosity." (ibid.) "And do not say before the angel" (ibid.) - this refers to the prayer leader who comes and tells you to give as you have decided, and you say, "There was a mistake, and I did not know what I was saying." Why should God be angry with you? It is because of the voice that you uttered and said to give, but did not give. (ibid.) "And ruin the work of your hands" (ibid.) - the commandments that were in your hands, you have lost.
Another interpretation of "Do not give your mouth" - Rabbi Levi said that this refers to the hypocrites. "Why should God be angry?" - it is because of the flattery that you utter with your mouth. "And ruin the work of your hands" - the little bargaining that you have in your hands, you mix them up. Another interpretation of "Do not give your mouth to sin against your flesh" - the sages said that it refers to Miriam, when she spoke against Moses and was struck with leprosy, as it is said (Numbers 12:1), "And Miriam and Aaron spoke against Moses."
And what happened to her? (ibid. 10) "And behold, Miriam was leprous, like snow." "Do not say before the angel" - this refers to Moses, as it is said (Exodus 20:16), "And he sent an angel and brought us out of Egypt." Was it really an angel? Rather, it was Moses.
"Why should He be angry?" - because of this voice that you flatter with your mouth. "And ruin the work of your hands" - the little effort that you have, you mix up." On the same voice that came out of her mouth about Moshe the righteous. "And the guilt of your hands."
These are the drums, as it is said (Exodus 15:20), "Miriam the prophetess, the sister of Aaron, took the drum." Another interpretation: speaking evilly, as they cause their flesh to sin by what they utter, they are punished with leprosy. "Do not say in the presence of the angel, this is the priest," as it is said (Malachi 2:7), "For the lips of the priest should guard knowledge, and they should seek instruction from his mouth."
The one afflicted with leprosy goes to him, as it is said (Leviticus 14:2), "This shall be the law of the leper." One who speaks evil and utters slander, as it is said (Leviticus 14:3), "And he shall be brought to the priest." Why would God be angry? Because of that voice that you uttered and spoke slander against your friend, and the guilt of your hands.
The little Torah that you have in your possession, you lose. And who was it who was worried and spoke evil of David and was afflicted with leprosy? As it is said (Psalms 41:6), "And if he comes to see me, he speaks falsehood; his heart gathers iniquity to itself; he goes out and speaks it." And what is meant by "he shall break down the house"?
It is like it says (2 Samuel 15:13), "And who caused him to do so? Because he spoke slander against David," as it is said (1 Samuel 22:9), "Then Doeg the Edomite, who was standing among Saul's officials, said, 'I saw the son of Jesse come to Ahimelek son of Ahitub at Nob.'"