Sardis (modern Sart, Turkey), in Roman times, was a wealthy city known for the manufacture and dyeing of woolen fabric and carpets. Originally, it was the capital of the ancient Lydian Empire and was the first city to mint coinage (600 B.C.). A stream that flowed through its market place carried gold dust from a nearby mountain. King Croesus of Lydia (560-546 B.C.) financed the building of the great Temple of Artemis in Ephesus (550 B.C.). The city was conquered twice, under Cyrus the Great and under Antiochus, due to lack of adequate watchfulness.
See note 1:4.
Philadelphia (modern Alashehir, Turkey) was a commercial center located on elevated ground overlooking the fertile plain of the Hermus (Gediz) River. In 189 B.C. the king of Pergamum established Philadelphia and named the city to honor his brother.
Like the common phrase “pillar of the community,” this is a metaphor of great honor, but far more so. The statement that the one who overcomes will never leave the temple is assurance that he will never lose the privilege of being in the presence of God and serving Him.
Laodicea, located beside the Lycus River, was a prosperous city about forty miles south of Philadelphia. It had a well-respected financial center, thriving textile production industry (specializing in black wool), and a leading medical school that produced a famous eye salve. Two other cities were in this general area: Colossae, known for its mountain spring of cold, fresh water; and Hierapolis, a site famous for its hot, therapeutic mineral springs.
I.e. Origin of Source.
This phrase and the word lukewarm in v 16 form a metaphor that is probably based on the quality of the water supply of Laodicea, which was delivered by aqueduct from the hot mineral springs about five miles away. During its journey, the water cooled to a warm or lukewarm temperature.
I.e. alive, productive--beneficial in one way or the other.