In Psalm 141:3 David prayed, “Set a guard, O Lord, over my mouth; keep watch over the door of my lips!” David prayed that he might use his mouth to impart blessings to those who hear, speaking the truth uprightly. Similarly, the lips of the priests were to guard knowledge. They were to use their lips to ensure that the knowledge of God, his will and way of salvation, was not lost, for God’s people are destroyed for lack of knowledge (Hosea 4:6). The priests were to ensure that true knowledge is not perverted with lies or half-truths. They were to speak the whole truth and nothing but the truth.
7 For the lips of a priest should guard knowledge, and people should seek instruction from his mouth, for he is the messenger of the LORD of hosts.