Knowing that calligraphy is poor, ghosts and gods are surprised. I don't know what it means to be poor enough to make ghosts laugh.

This means that if you know the inner secret and the formula of Buddhism in calligraphy, the power of this kind of spell is frightening to ghosts and gods, so this kind of spell can serve ghosts and gods. On the other hand, if you don't know the inner secret and the formula of Buddhism, you will make ghosts and gods laugh at you!