This artwork draws its inspiration from the book of Joshua, where Joshua, son of Nun, sent two spies to Jericho; before Israel seize the first city in the promised land. The destruction of Jericho is a miracle.
A promise is always most treasured when you are down and out. When you are at your lowest, you cannot imagine happiness. That is why we need to have a mental image that gives us hope. Israel had been in exile when Jeremiah gave this promise from God. So I imagine that their mental image is the land which was promised to them in Joshua 1 – where God promises to bring them back to their homeland.