There were a lot of code words which Christians used, and this so they could practice their religion safely, exchange letters, and so the gentiles wouldn’t learn about the mysteries, because they knew that, if the gentles ever learned about the mysteries of their faith, they (the mysteries) would be ridiculed and mocked by those who do not understand them. The Christians certainly did preach about Jesus, but of the msteries, only the catechized were allowed to learn about them. Because of this, in the ancient world Christianity was kind of looked at as a secretive religion.
The Book of Revelations uses many symbols which were familiar to Christians, especially Christians who converted from Judaism (many Christian symbols were actually borrowed from Judaism). I can list a few of the symbols used by Christians, but not all of them, since symbolism isn’t my area of expertise.
Fish - Jesus
Babylon - Rome
Woman - God’s People, the Virgin Mary
666 - Emperor Nero
Bread - Manna, Jesus
Vineyard - Israel
Jerusalem - Paradise