The ancient city of Philadelphia was named out of brotherly love by Eumenes II of Pergamon for his brother Attalus II. It was handed over to Romans after Attalus III since he did not have an heir to succeed. The modern name for Philadelphia is Alasehir.
The below picture shows the position of ancient Philadelphia in the modern map.
The city of Philadelphia suffered a huge loss during the earthquake in AD 17. Roman Emperor Tiberius gave tax exemption to the city and in return of honor, the city proved its allegiance to the Roman emperors by printing the emperor's face in their coins. The church of Philadelphia along with Smyrna did not receive any call for repentance or warned of punishment. They were commended for their faithfulness for holding on to the word and offered protection during the hours of testing (3:10).
Based on the text from Revelation (3:8, 3:10) the church went through a period of persecution due to the imperial cult (emperor worship) enforced by the Roman kings. In spite of persecution the church received an open door from Jesus, which nobody can shut as a reward to their perseverance and for not denying the name of Jesus. In the message to Philadelphia, the condemnation is directed towards Jewish Synagogue, who might have pointed their fingers towards Christians and excluded them from the immunity they enjoyed to imperial worship.
Philadelphia along with Smyrna did not receive any call for repentance or warned of punishment.The Church of Philadelphia would understand the context of the pillar in the temple of God (3:12) than anybody else with their fresh memories on the devastating earthquake.
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