Activating the Textures in Game
Once the pack is in your resourcepacks folder, you need to enable it from the in-game menu so the updated bookshelf visuals load properly.
1. Open the pause menu or main title screen and select Options.
2. Click Resource Packs to view your installed packs.
3. Hover over the Retextured Bookshelf Resource Pack in the left Available column and click the arrow to move it into the right Selected column.
4.
Fixing Load Order Conflicts
If your standard bookshelves still show default wood tones or another pack's textures, another active resource pack is overriding these files. Minecraft loads resource packs from bottom to top, giving highest priority to whichever pack sits at the top of the Selected list.
1. Return to Options > Resource Packs.
2. Find Retextured Bookshelf Resource Pack in the right-hand list.
3. Click the up arrow on its icon until it sits above any full texture overhauls or building packs.
4. Click Done to reload, then place a regular bookshelf next to a chiseled bookshelf to confirm their wood color palettes now match.