He speaks through the mouth of his young prophet Jeremiah, who must pass the words on to Jerusalem, literally it says: read (ESV: proclaim). This also means that Jeremiah must have everything written down. He had a secretary for that, Baruch (read about this in Jeremiah 36:4–6). The purpose of this reading is that the people will turn to God again.
2 “Go and proclaim in the hearing of Jerusalem, Thus says the LORD, “I remember the devotion of your youth, your love as a bride, how you followed me in the wilderness, in a land not sown.