OK, rizen1: generally these 7 letters are dictated to John who writes as a secretary here taking down the words that the Glorious Christ of ch.1 tells him to write. Our LORD follows a pattern in each of them. In the 1st part there is a reference to some aspect of His character that introduces the personal capacity that Christ is addressing them in. Next there is some kind of recognition given to their present estate, commendation and/or reprimand. Thirdly, there are recommendations and warnings; followed by promises for overcoming (so I take it that there is a struggle laying behind each of these addresses for each of the individual assemblies). These conflicts are the prototypical struggles of all assemblies, at all times, in the battle zone of this life (as indicated by B-A-C). And then fifthly, there is an invitation to all assemblies to hear what the Spirit says to each one of them: ch3: "22 He that hath an ear, let him hear what the Spirit saith unto the churches." Thus showing each letter's relevance for all churches, the original 7, and all others as well.
Referring back to chapter 1, you have a visual picture of Christ walking amidst His assemblies; He walks in such a way today, never neutral to our affairs, but always in His purity commending , reproving, pointing out, warning, comforting, and promising retribution or reward. The temporal affairs of His assemblies are reflections of His glory one way or the other. He brings them into existence and He can take them out; churching together is a very serious thing; His name is at stake.
As to "synagogue of Satan" it is not mysterious language; it is simple descriptive language. Everyone knows what a synagogue is: our LORD taught in them; Paul sought them out in his travels as the first place to start his proclamation of the gospel; in Corinth, as the synagogue hardened to the cross of Christ, members were thrown out and formed the assembly there, "the church of Corinth"; there was also a synagogue in Ephesus before the believers, both Jew and Gentile, were separated; if the city had no synagogue, as in Philippi, Jews and proselytes met at a convenient water course: "Acts 16:13 And on the sabbath we went out of the city by a river side, where prayer was wont to be made; and we sat down, and spake unto the women which resorted thither." Now this last is a rudimentary synagogue, according to tradition it took 10 members. When in history a synagogue became the enemy of the cross of Christ and adopted the rule that as to Jesus of Nazareth: God has not come in the flesh and thus denying the Son of God, then at that time they became a synagogue of Satan. Antichrist and the spirit of antichrist at that time was already in the world: 1Jn.2:18 "Little children, it is the last time: and as ye have heard that antichrist shall come, even now are there many antichrists; whereby we know that it is the last time." And the test, a few verses later was: "22 Who is a liar but he that denieth that Jesus is the Christ? He is antichrist, that denieth the Father and the Son. 23 Whosoever denieth the Son, the same hath not the Father: he that acknowledgeth the Son hath the Father also." This is the same way our LORD spoke to the temple and synagogue religious leaders when He was in their cities: Jn.8:43 "Why do ye not understand my speech? even because ye cannot hear my word. 44 ye are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it."
So, it is apparent that at this time in history these synagogues had so ruled. The one in Philadelphia, however would be brought to realize the truth: that God was with the small despised assembly that honored Christ name and kept His word; there would be a struggle in their evangelism however, but they had an open door no one could shut. "7 And to the angel of the church in Philadelphia write; These things saith he that is holy, he that is true, he that hath the key of David, he that openeth, and no man shutteth; and shutteth, and no man openeth; 8 I know thy works: behold, I have set before thee an open door, and no man can shut it: for thou hast a little strength, and hast kept my word, and hast not denied my name. 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. 10 Because thou hast kept the word of my patience, I also will keep thee from the hour of temptation, which shall come upon all the world, to try them that dwell upon the earth. 11 Behold, I come quickly: hold that fast which thou hast, that no man take thy crown. 12 Him that overcometh will I make a pillar in the temple of my God, and he shall go no more out: and I will write upon him the name of my God, and the name of the city of my God, which is new Jerusalem, which cometh down out of heaven from my God: and I will write upon him my new name. 13 He that hath an ear, let him hear what the Spirit saith unto the churches." This particular synagogue of Satan would have it gates blown away by the preached gospel and its prisoners freed.
I hope this helps some; it is a straight forward interpretation, not at all a novel one. And I do think it is the most simple and obvious.
