Experienced InDesign users know the value of using Layers on complex documents, particularly ones where text, object and image items are stacked on top of each other.
One handy shortcut is the ability to select all items on any particular layer, which you can do by either Option + Clicking the name of the Layer in the Layers panel, or by clicking the Item Indicator square on the far right of the Layer in the list. Performing either action will select all the items on that particular layer.
Now let’s say you want to move all the items from one layer to another. Simple. Just click that little Item Indicator square of the layer you want to move FROM and drag it to the layer you want to move it TO.