Who is this synagogue of Satan that is spoken of in Rev 3:9? “I will make those who are of the synagogue of Satan, who claim to be Jews though they are not, but are liars–I will make them come and fall down at your feet and acknowledge that I have loved you.”
For about the first 20 years after the cross, the Church was made up almost exclusively of Jews. Many of these were Pharisees who had been around the Temple when the veil was rent on the day of the Lord’s death.
Some of them were convinced that the Old Covenant Laws were still in effect, and that Gentiles who wanted to follow the Lord had to enter Christianity through Judaism. More and more Gentiles began accepting Jesus as their Savior and so the Apostles held a meeting in Jerusalem to settle the issue. (Acts 15:1-21) Did a Gentile have to become a Jew, subject to the Law, before he could become a Christian? James, the brother of the Lord and head of the Church in Jerusalem said, “No” and from that time forward Gentiles could come straight into Christianity.
But there were false teachers who followed Paul around, and after he left a place they would try to undo his work by telling the Gentiles they had to become Jews first and that Paul had left out this requirement to trick them. This happened in many of the Gentile communities, including Philadelphia. These false teachers were called “Judaizers” and are the synagogue of Satan to which the Lord referred.
There are still those who teach that the Lord’s death and resurrection are not sufficient to guarantee a believer’s place in heaven. They teach that believers must also maintain a certain standard of behavior after becoming saved, and if they don’t then the Lord will revoke their gift of salvation, leaving them lost and without hope. We don’t call them Judaizers anymore, but their intent is the same, to try and make expensive that which the Lord gave His life to make free.
Others teach that the Church has inherited the promises to Israel and that the references in the Bible referring to Israel’s future are really intended for the Church. By claiming the promises to Israel, they’re in effect claiming to be Jews though they’re not. Since the seven letters have a prophetic application as well as an historical one, I believe the Lord was also including these groups in His letter to Philadelphia.