Revelation 3:7–13 contains Jesus’ letter to the church at Philadelphia. Philadelphia, was a center for exporting the Greek language and culture into the interior of Asia Minor. Thus, it had a secular missionary calling. Just as the city had an open door to the interior, so the church had an open door to spread the gospel. Jesus commends the church in verse 10 and promises to keep it from the tribulation period. He also instructs the church to retain the truth and promises each conqueror special recognition in the New Jerusalem. Smyrna and Philadelphia are the only churches in Revelation not to receive any particular criticism. The church at Philadelphia’s characteristics are similar to those of the Church in the 19th and 20th centuries that was a period of frequent revivals and missionary activity.
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“Revelation 3:11” Bibleref.com
11 I am coming quickly! Hold firmly that which you have, so that no one takes your crown.