Behold I give of the synagogue of Satan. The true reading seems to be neither δίδωμι nor δέδωκα, but διδῶ, from the form διδόω, which is fairly common in classical Greek. The construction, ἐκ τῆς συναγωγῆς, the partitive genitive used as subject or object of a verb, is frequent in St.
John's writings (John 1:24; John 7:40; John 16:17; 2 John 1:4; comp. John 6:39; John 21:10). The Church of Smyrna was encouraged with a promise that their Jewish opponents should not be victorious over them.
The Philadelphian Christians are told that they shall be victorious over their Jewish opponents. As before (Revelation 2:9), those who "say they are Jews, and they are not," are Jews who refuse to believe in the Messiah and reject the Gospel.
The only true Jews are those who accept the Christ. They are not, but do lie. Antithetic parallelism, as in verse 8 and Revelation 2:13. I will make them to come and worship at thy feet. This would be fulfilled when the destruction of Jerusalem drove large numbers of Jews into Asia Minor.
Every city which had previously had a Jewish colony would then receive a great influx of refugees. This augmented Jewish settlement at Philadelphia was to furnish some converts to the Christian Church; but, as we learn from the epistles of Ignatius, these converts tainted the Church with a stubborn form of Judaistic error.
Hence the need of the warning in Revelation 2:11. Compare "The sons also of them that afflicted thee shall come bending unto thee; and all they that despised thee shall bow themselves down at the soles of thy feet" (Isaiah 60:14; Isaiah 49:23).
Know that I have loved thee. The "I" is emphatic: "I will cause them to recoginize that in this you received a blessing manifestly Divine."