Don't leave this area of the library just yet. Click on the radio which can be found in the background (screen). Wait for the game to zoom in the view on the radio. You should be able to notice an Angel in the upper right corner of the screen. Pick it up and close this window. Finally, choose a passageway located to the left of the stairs (it leads to the fireplace).
You will have to perform two actions here. Use the handwheel (screen) and you'll notice that the chandelier has been lowered a little (you will be rewarded with a short cut-scene). After that, pick up a Poker. You may go back to the main area of the library.
Try clicking on the lowered chandelier and listen to what Van Helsing has to say about this object. Now you will have to click on a Rolling staircase (screen) which you weren't able to interact with before. I guess you might be surprised a little to actually find this object in your inventory. Choose the staircase and use it on the chandelier. As a result, Van Helsing will place the staircase directly under this object.
Now you will have to click on the ladder. This will allow Van Helsing to get closer to the chandelier. You'll be given a chance to have a closer look at this object. All you have to do here is to pick up a new Angel figure (screen). Go back to the ground level.
Go back to the area where you found the puzzle with angels and demons. Open your inventory and choose a poker. Combine this object with the braces taken from the skeleton. Choose this completely new device and click on one of the jars (screen). Once this is done, take tweezers and use them to acquire the final figure from the jar, representing a Demon.
Now you may finally go back to the panel with angels and demons. Since you've got all the figures in your possession, you will have to start placing them in the main field (screen). It shouldn't take you too long, especially since the game will prevent you from placing a figure in an incorrect spot. A passageway will open, granting you access to the abbey.