God continues His response to the prophet with a stunning rebuke, one which contains more than a veiled threat.
This translation masks the moment—the import—of God's words. He is warning Jeremiah that he must return, that is, repent, abandoning “this mistaken tone of distrust and despair,” as The Amplified Bible glosses verse 19. God promises He will restore him as His prophet, the “mouth” of God, only if he comes to understand the difference between the precious way of God and that vile way of the wicked.
The Living Bible better conveys the import of God's comments to Jeremiah with this paraphrase of verse 19:
Stop this foolishness and talk some sense! Only if you return to trusting me will I let you continue as my spokesman.
The Message handles the same passage this way:
Take back those words, and I'll take you back.
Then you'll stand tall before me.
Use words truly and well. Don't stoop to cheap whining.
Then, but only then, you'll speak for me.
The Good News Translation presents this paraphrase:
If you return, I will take you back, and you will be my servant again. If instead of talking nonsense you proclaim a worthwhile message, you will be my prophet again.
It is clear that God is not mincing His words. In this time of crisis for Judah, God demands a servant in whom He can have confidence, one who will fearlessly warn in the face of persecution and who will remain committed to carrying out His work to its conclusion—no matter where that work may take him. God needs an individual of resolute and indefatigable faith.
Actually, God is telling Jeremiah that his office of prophet is on the line. He absolutely must overcome his doubts of God's fidelity. He must not fall back into the ways of the people of Judah. He can only continue to be separate from them by believing God.