The NASV uses "dread" rather than fear. Either way it is that fear, that dread, which, unlike terror, should have been a spur to devotion along with thankfulness. Thankfulness for all that God had done in bringing them into the good land and making their stay there profitable, and fear/dread because God does not leave the sinner unpunished, nor does he withhold the consequences of our sins from us (col 3:25 For the wrongdoer will be paid back for the wrong he has done, and there is no partiality.).
But they were no longer thankful and they no longer feared God; they had forgotten what he had done and they had forgotten who he was. V13 [for my people have committed two evils: they have forsaken me, the fountain of living waters, and hewed out cisterns for themselves, broken cisterns, that can hold no water.] they had forgotten and forsaken God; treated him as worthless and walked away from him. AND they had proceeded to create something to replace him. God who is the source of life, both physical and spiritual, is disregarded and the people construct not so much a source of life as a container. For a cistern is a container more that it is a fountain. A cistern receives and holds. A fountain produces. But this cistern is broken; that which it receives leaks out and is lost.
This is so like our modern world. Being no longer content to accept that God made the universe and all it contains, we have forsaken his revelation in favour of our own naturalistic one. In the beginning there was nothing, and then it exploded. Can this explanation of all we see and experience give us life? No. It is a broken cistern for it is neither true nor consistent and the thought culture that it produces has for years been used as a way for the powerful to amass power and to control and destroy the powerless. 'The fittest survive; we think we are the fittest therefore we are going to survive and you aren't.'
The Israelites had forgotten God and replaced him with a mythology of their own devising -- an eclectic mix of Egyptian and Assyrian mumbo-jumbo [v18] -- and enough of the forms (but without the substance) of Judaism to give it the appearance of validity. These were the same people who would go on to worship the bronze snake.
21st century people fancy themselves wise and enlightened and no longer under the sway of myth and falsehood [echoing the sentiments of Jer 2:31b "We are free, we will come no more to thee"]. Sadly this is not the case. If Jesus does not come back for another thousand years there will be those who will look back upon our time and write books about the myths and legends of the 21st century. Top of the list will be a fairy story called Evolution.
We are no longer willing to "hear the word of the Lord" preferring the word of scientists and other self-confessed experts. We are proud: Proud of our accomplishments and our technology; Proud of our control over the forces of nature (small as that control really is against the might of cyclone, earthquake, flood and volcano.)
Similarly the Israelites, no longer content with the revelation of God, concocted their own. And that offended God, deeply.
For as much as Jeremiah may be a book about a man thrown in at the deep end, it is also a book about the wisdom of God and the foolishness of mankind. God is to be feared. That fear is such that it drives out all other fears. We are also to love God but too often we confuse love with "in love" and the emotional rollercoaster of infatuation. The "love" that God calls us to is more profound, more deliberate than that. Fear is not out of place in that love. Dread is not out of place in that love. For that love implies a devotion which may cost us in the short term. That love may even lead us into pain, suffering and death. It certainly led Jeremiah into pain and suffering. It led Paul into suffering Acts 9: 15, 16 'But the Lord said to [Ananias], “Go, for he is a chosen instrument of mine to carry my name before the Gentiles and kings and the sons of Israel; for I will show him how much he must suffer for the sake of my name.”'