Legal Question in Credit and Debt Law in California

It depends. If the city allows other preachers from other religions to sermonize, no. If the city does something to prefer one religion over another, then maybe yes.

Mr. Stone is sort of right. It's a bit more complicated than that, and depends on a lot of factors such as whether permits are required and granted, what activities may or may not accompany the sermon, etc. If someone just walks into a park and gives a sermon, however, and anyone else who walks into the park can give a speech on a topic of their choice, then it definitely would not violate the separation of church and state.