There were many Jews dispersed across Asia Minor and elsewhere in the days of the apostles (see, e.g., Acts 13:14, Acts 13:43; Acts 14:1, Acts 14:19; Acts 16:3), with numerous towns having a synagogue (a meeting place) where the Jews gathered on the Sabbath. Clearly there was a synagogue in Philadelphia too. But the Jews habitually gathering in this synagogue, says Jesus, are not real Jews but are followers of Satan (see also Revelation 2:9). True Jews would desire to welcome the arrival of the great Son of David. But these Jews rejected Jesus Christ in unbelief and so showed themselves to be in league with Jesus’ great adversary, Satan.
9 Behold, I will make those of the synagogue of Satan who say that they are Jews and are not, but lie behold, I will make them come and bow down before your feet, and they will learn that I have loved you.