Lamentations 3:22–23 was written from inside Jerusalem's complete destruction — the temple burned, the people exiled, everything lost. The author does not explain why God allowed it. He does not construct a theodicy. He holds onto one thing: "It is of the LORD'S mercies that we are not consumed, because his compassions fail not. They are new every morning: great is thy faithfulness." The morning renewal of mercy is not a feeling. It is a theological claim made in the worst possible circumstances. Divorce recovery often means surviving one morning at a time.
Isaiah 43:18–19 tells a people stuck in their worst chapter to stop looking backward: "Remember ye not the former things, neither consider the things of old. Behold, I will do a new thing." The new thing is not described as better in all respects than the former thing. It is described as something that requires active perceiving: "shall ye not know it?" God is doing something new; the question is whether you will notice it.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.