In the letters to the early Christian churches of Smyrna and Philadelphia in Revelation 2:9 and 3:9, reference is made to a synagogue of Satan (Greek: συναγωγή τοῦ Σατανᾶ, synagoge tou satana), in each case referring to a group persecuting the church "who say they are Jews and are not". In Revelation 2, the Smyrna church is advised not to fear the events they are about to suffer; in Revelation 3, the Philadelphia church is promised that the persecutors will "come and worship before [their] feet, and ... know that I have loved you".
The phrase is also used in a fragment of a lost work on Dioscorus I of Alexandria found at the Monastery of Saint Macarius the Great in 1923 and identified by American theologian William Hatch.[1] Hatch believes the term refers to the Council of Chalcedon, which Dioscorus attended in 451 and from which he was deposed and exiled for his monophysite Christology.
Revelation 3:9 (KJV)
“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.”
SYNAGOGUE OF SATAN - Full documentary
The phrase is also used in a fragment of a lost work on Dioscorus I of Alexandria found at the Monastery of Saint Macarius the Great in 1923 and identified by American theologian William Hatch.[1] Hatch believes the term refers to the Council of Chalcedon, which Dioscorus attended in 451 and from which he was deposed and exiled for his monophysite Christology.
https://en.wikipedia.org/wiki/Synagogue_of_SatanRevelation 3:9 (KJV)
“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.”
SYNAGOGUE OF SATAN - Full documentary