I believe that what they called “superstition”.
Believing in something that’s not real with some sorts of entities of the “spirit-kind”.
Spirits, ghosts, deities, angels, demons, jinns, shen, deva/devi, Brahman, kami, fairies, etc, are just some of superstitious beliefs.
Although Jesus supposedly taught to the masses in Galilee and Judaea, he didn’t write any of the gospels, letters and apocalyptic texts in the New Testament.
Much of church survival was dependent on Paul’s teaching, who never met Jesus who was described in those gospels.