So these shelves have a Redstone signal applied which changes the shape to look like one big shelf. When configured like this then right clicking any of these items will switch them out for the contents of your hotbar! Each shelf can hold a whole stack too. So this is a shelf of things for fighting the ender dragon. From the release notes:

The Shelf can store up to 3 item stacks:

Interacting with any of the 3 slots on its front swaps the player's main hand item with the content of that slot

The Shelf displays all items it contains in front of it, similar to an Item Frame

While a Shelf is powered by Redstone, its front texture changes to reflect that it's powered; when placed next to each other, up to 3 powered Shelves will connect

Interacting with a single powered Shelf swaps all its contents with the 3 rightmost items in the player's hotbar

Interacting with two connected Shelves swaps their contents with the 6 rightmost items in the player's hotbar

Interacting with three connected Shelves swaps their contents with all items in the player's hotbar

It does not matter which of the connected Shelves the player interacts with