The Church In Philadelphia
Philadelphia, from the Greek word (pronounced) fil-ad-ale-fee-awh, was an ancient city in Lydia (a province in western Asia Minor i.e. Turkey). It was founded approximately 159-138 B.C. by Attalus II Philadelphus of Pergamum and named from the king's love for his brother Eumenes II. In the original Greek, the word means love for a brother, whether a sibling, or in a larger sense, affiliation (the "phil" in Philadelphia and the "fil" in affiliation have the same root).
Due primarily to the efforts of the apostle Paul (who was also born in Turkey, at Tarsus), Christianity at first grew most widely, on its way to Europe, through Turkey (see Paul's First Missionary Journey, Paul's Second Missionary Journey and
Paul's Third Missionary Journey). Local churches of the one and only true Church of God were founded there, including at Philadelphia. It was to seven of those local groups that Jesus Christ addressed the book of Revelation:
"1:1 The Revelation of Jesus Christ [see Apocalypse], which God gave unto him, to show unto his servants things which must shortly come to pass; and he sent and signified it by his angel unto his servant John" (Revelation 1:1 KJV)
"1:11 Saying, I am Alpha and Omega, the first and the last: and, What thou seest, write in a book, and send it unto the seven churches which are in Asia; unto Ephesus, and unto Smyrna, and unto Pergamos [i.e. Pergamum], and unto Thyatira, and unto Sardis, and unto Philadelphia, and unto Laodicea." (Revelation 1:11 KJV)
"He that hath an ear, let him hear what the Spirit saith unto the churches"
The "seven churches" were contemporary in existence, not successive. What was spoken to them by Christ were lessons in behavior to everyone, that each of the seven displayed most i.e. each was an example of something good or bad (see Christian Living).
"3:7 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;
3:8 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.
3:9 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. 3:10 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.
3:11 Behold, I come quickly: hold that fast which thou hast, that no man take thy crown.
3:12 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 [see The Throne Of God, From Heaven To Earth]: and I will write upon him my new name.
3:13 He that hath an ear, let him hear what the Spirit saith unto the churches." (Revelation 3:7-13 KJV)
Fact Finder: What is meant by "the synagogue of Satan" as stated in the verses quoted above?
See The Synagogue of Satan; also The Messiah's Synagogue