Jeremiah doesn’t hold anything back when he promises Israel that just as the blessings of the covenant promises God made with Israel were theirs for many years, so too will the curses for breaking the covenant will now be theirs 
for many years. Yet God, once again, leaves them a promise of hope. Jeremiah 5:18 says, “But even in those days, declares the LORD, I will not make a full end of you.” I like the way Hall explains this verse. He writes, “Verse 18 repeats for the third time, I will not make a full end with you (cf. 4:27; 5:10); it is the one ray of hope in an ominous sky. Out of the destruction of the nation and the city, God would preserve a remnant. Jeremiah with clear vision had his eyes upon Bethlehem and Calvary.”[1] This will become even more obvious when you study the New Covenant passages of Jeremiah 31. This is the covenant that Jesus established in His blood at the last supper. God will make a new arrangement with people in that New Covenant. God never leaves His people without a ray of hope. That’s why He sent His Son into a hopeless world.
If there is anything we learn from studying the life of Jesus is that He is the ray of hope for the entire world. Just remember His life on earth. When the blind man had given up any hope of ever seeing again, he heard about Jesus. When the women who had been sick for nearly 20 years lost all hope of healing, she heard about Jesus. When the 10 lepers declared unfit to live in society had given up all hope of ever joining with the human race again, they heard about Jesus. When the crippled man at the pool of Bethesda had given up all hope of healing, along came Jesus. When Martha and Mary had given up hope about their brother’s sickness and buried him Jesus showed up on the scene. He brought with him hope! The New Covenant is all about hope for broken sinners.
I like to think of the phrase “I will not make a full end of you.” We will all lose loved ones. We will all experience unexplainable painful circumstances. We will all experience a sickness that will end in our deaths, but God says, “I will not make a full end of you.” My favorite Easter passage is 1 Peter 1:3. It says, “Blessed be the God and Father of our Lord Jesus Christ! According to his great mercy, he has caused us to be born again to a living hope through the resurrection of Jesus Christ from the dead, to an inheritance that is imperishable, undefiled, and unfading, kept in heaven for you.”
[1] Bert Harold Hall, “The Book of Jeremiah,” in Isaiah-Malachi, vol. 3, The Wesleyan Bible Commentary (Grand Rapids, MI: William B. Eerdmans Publishing Company, 1969), 200.