REPENT Jeremiah 15:19

Therefore this is what the LORD says: "If you repent, I will restore you that you may serve me; if you utter worthy, not worthless, words, you will be my spokesman. Let this people turn to you, but you must not turn to them."

If you repent 
Jeremiah 3:12-14  "Go, proclaim this message toward the north: 'Return, faithless Israel,' declares the LORD, 'I will frown on you no longer, for I am faithful,' declares the LORD, 'I will not be angry forever. Only acknowledge your guilt--you have rebelled against the LORD your God, you have scattered your favors to foreign gods under every spreading tree, and have not obeyed me," declares the LORD. "Return, faithless people," declares the LORD, "for I am your husband. I will choose you--one from a town and two from a clan--and bring you to Zion."
Jeremiah 3:22  "Return, faithless people; I will cure you of backsliding."  "Yes, we will come to you, for you are the LORD our God."
Jeremiah 4:1-2  "If you, Israel, will return, then return to me," declares the LORD. "If you put your detestable idols out of my sight and no longer go astray, and if in a truthful, just and righteous way you swear, 'As surely as the LORD lives,' then the nations will invoke blessings by him and in him they will boast."

I will restore you that you may serve me 
Jeremiah 3:7  "This is what the LORD Almighty says: 'If you will walk in obedience to me and keep my requirements, then you will govern my house and have charge of my courts, and I will give you a place among these standing here.' "
Numbers 16:8-11  Moses said to Korah, "Now listen, you Levites! Isn't it enough for you that the God of Israel has separated you from the rest of the Israelite community and brought you near himself to do the work at the LORD's tabernacle and to stand before the community and minister to them? He has brought you and all your fellow Levites near himself, but now you are trying to get the priesthood too. It is against the LORD that you and all your followers have banded together. Who is Aaron that you should grumble against him?"
Deuteronomy 10:8  At that time the LORD set apart the tribe of Levi to carry the ark of the covenant of the LORD, to stand before the LORD to minister and to pronounce blessings in his name, as they still do today.

if you utter worthy, not worthless, words, you will be my spokesman 
Exodus 4:16  "He (Aaron) will speak to the people for you, and it will be as if he were your mouth and as if you were God to him."
Jeremiah 1:9  Then the LORD reached out his hand and touched my mouth and said to me, "I have put my words in your mouth."

(parentheses are mine)

Scriptures taken from the Holy Bible, New International Version® NIV®, Copyright© 1973, 1978, 1984, 2011 by Biblica, Inc.® Used by permission. All rights reserved worldwide. 
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