Jeremiah 15:19
Therefore thus saith the LORD, If thou return, then will I bring thee again, and thou shalt stand before me: and if thou take forth the precious from the vile, thou shalt be as my mouth: let them return unto thee; but return not thou unto them.
God calls for a clear separation of what is precious, holy and true from what is vile, false and spurious, keeping the two distinct and never treating them as alike. This matters because deception succeeds by mingling truth and value with evil, so a bright and heavenly appearance does not make a teaching trustworthy, and wisdom mixed with error, superstition and human tradition in books, teachers and pagan or infidel sources must be discerned and rejected in favor of truth sought in God's word. Failing to make that difference between truth and error is itself evidence of deception, and when it is not made the world is given over to delusion. The same separation divides people when truth demands decision, separating honest believers who receive it from the corrupt who reject it, and requiring the church to correct unchristian lives or separate the unrepentant so God may have a clean people. Whoever returns to God and does this separating work will stand before Him and speak as His mouth, which requires a cleansed life and Spirit-guided speech that reforms and heals rather than mixing sacred truth with harshness, self, provocation or poison.
Separating Precious from Vile
Jeremiah 15:19 commands a clear distinguishing of what is precious, holy and true from what is vile, false and spurious, keeping the two distinct instead of treating them as alike. That work must be carried out faithfully even when some of the instruments used are unholy or unfaithful. Failure to make that difference between truth and error is evidence of deception, as seen when Thomas Paine, an enemy of God and His law, is presented as exalted in heaven and teaching alongside the apostles. When no such difference is made between truth and error, the world is given over to delusion.
Deception is able to work in this way because Satan knows both good and evil and mingles truth and value with evil in order to deceive. In education this means discerning in books and teachers where error, superstition and human tradition are mingled with true learning and knowledge, a mixture that can become spiritually harmful. A bright, heavenly appearance does not make a source trustworthy, so teachings produced by Satan's agents and pagan or infidel writings are not to be accepted or recommended as essential or valuable merely because they contain some wisdom. Truth is instead to be sought in God's word, where it has been buried beneath human tradition and opinion, rather than drinking from polluted sources.
The verse also describes a separation of people when truth calls for a decision, in which those who receive the truth are separated from the corrupt who reject and neglect it, and that response itself makes the separation between honest believers and those who refuse the truth. For the church this means showing those who live unchristian lives their wrongs, and if they do not correct them, separating them from the faithful so that God may have a clean and pure people. Doing this work of separating the vile from the precious is part of being a co-worker with the Third Angel, a work in which Brother Ross had failed.
Returning to Speak for God
If a person turns back, God will bring him back again to stand before Him, and if he takes forth what is precious from what is vile he will be as God's mouth. This upholds the minister's calling to be God's mouthpiece, a responsibility that requires a life worthy of speaking for Him.
Serving as God's mouth applied to speech means cleansing away natural, harsh habits and speaking so as to reform and heal rather than to provoke or poison others. Becoming fit to speak for God requires putting away natural, self-driven ways and speaking the truth under the Holy Spirit's influence. Words spoken in that Spirit reform and heal, and do not poison, offend, or stir hearers to rebellion. Sacred truth must not be mingled with harshness or self.