Malachi 2:7
For the priest’s lips should keep knowledge, and they should seek the law at his mouth: for he is the messenger of the LORD of hosts. For the priest’s lips should keep knowledge, and they should seek the law at his mouth: for he is the messenger of the LORD of hosts.
The priest's lips are to preserve and guard knowledge and teach God's law, and the people are to seek instruction in the law from his mouth, because he is the messenger of the LORD of hosts. Keeping knowledge means keeping it ready to speak, not merely retaining it in the mind. As God's appointed messenger he must receive instruction from God and share what he knows as a sacred trust rather than withhold it.
The people's part is to seek the priest's counsel, ask him questions, and thereby gain a clear understanding of the truth. He must be ready to give a word from the Lord when needed, grounded in Scripture and spoken truthfully. That readiness includes always speaking of the good and beautiful things of God and His goodness. It draws on both old and new things, and continually presents the covenant of peace God made with Israel.
In context the faithful priest described by the surrounding verses has the law of truth in his mouth with no iniquity in his lips. He fears God, walks with Him in peace, equity, fairness and integrity, and turns many away from sin and iniquity. By contrast, priests who depart from the way, corrupt the covenant, cause people to stumble at the law, and treat it partially fail this duty.
This faithful ministry belongs to Levi's covenant of life and peace, given for reverent fear of God's name. It is lived out as consistent, loving, lovable Christianity that wears the beauty of Christ's heavenly character in the home life as the most powerful argument for the truth. It is fulfilled when the heart is saturated daily with the holy oil emptied from the two olive trees by looking unto Jesus and catching the light of His countenance and righteousness. Then the tongue speaks praise to God, sullenness, deformity of character and many words are turned into sound words, and the mind thinks on whatever is true, honest, just, pure, lovely, and of good report. For God's messenger this means turning time and talents away from political questions to represent Christ, living separate from the world with citizenship above and purified character.