I've only really started learning about that over the last year or so. I always thought the following verses were symbolic, but I'm learning that they might be litteral.

I know thy works, and tribulation, and poverty, (but thou art rich) and I know the blasphemy of them which say they are Jews, and are not, but are the synagogue of Satan. Revelation 2:9

Behold, I will make them of the synagogue of Satan, which say they are Jews, and are not, but do lie; behold, I will make them to come and worship before thy feet, and to know that I have loved thee. Revelation 3:9 KJV