When teaching primary teachers the importance of being prepared and knowing their lesson material relate it to the cake, which is on display. Talk about how desirable it is, how it took time to prepare it and make it. Compare this to the lesson manuals and helps put out by the church for teaching. They are desirable and someone has gone to much time to prepared them for us to present.
Then ask if any would like to have a piece of cake. (They may think you've tampered with it to make it taste bad, assure them it is as delicious as it looks)
When you have a volunteer to sample look about for a cutting utensil, plate, napkin, etc. Excuse yourself for not being prepared with these things and then just grab a handful of cake and hand it to the person. They will probably pull back and not accept the cake.
Compare this to the lesson manuals prepared for us. They are desirable and attractive but it is up to us to prepare them so that they are presented in the way they were meant to be. This is VERY effective. Enjoy!