Sardis: “He who overcomes will be arrayed in white garments …” (The Letters to the Seven Churches, pg. 13).

“Sardis … the capital of the ancient kingdom of Lydia … was situated in the middle Hermus valley at the foot of Mt. Tmolus, a steep and lofty spur of which formed the citadel. … Once at least, under the emperor Tiberius, in A.D. 17 it was destroyed by an earthquake; but it was always rebuilt, and was one of the great cities of western Asia Minor till the later Byzantine time. … Its importance was due, first to its military strength, secondly to its situation on an important highway, leading from the interior to the Aegean coast, and thirdly to its commanding the wide and fertile plain of the Hermus.”

“Sardis,” The Encyclopaedia Britannica, Vol. 24, p. 217.

The church at Thyatira allowed a woman who called herself a prophetess (the Lord did not call her one) to teach the above mentioned heresies from a position of authority. (The Letters to the Seven Churches, pg. 13).

“Thyatira was specially noted for the trade guilds which were probably more completely organized there than in any other ancient city. Every artisan belonged to a guild, and every guild, which was an incorporated organization, possessed property in its own name, made contracts for great constructions, and wielded a wide influence. Powerful among them was the guild of coppersmiths; another was the guild of the dyers, who, it is believed, made use of the madder-root instead of shell-fish for making the purple dyestuffs. A member of this guild seems to have been Lydia of Thyatira, who, according to Acts 16:14 , sold her dyes in Philippi. The color obtained by the use of this dye is now called Turkish red. The guilds were closely connected with the Asiatic religion of the place. Pagan feasts, with which immoral practices were associated, were held, and therefore the nature of the guilds was such that they were opposed to Christianity. … It was taught by many of the early church that no Christian might belong to one of the guilds, and thus the greatest opposition to Christianity was presented.”

“Thyatira,” International Standard Bible Encyclopedia.

“But the same evil practices taught in ‘the doctrine of Balaam,’ which were accepted by a few in Pergamum, were countenanced in the leadership of the church in Thyatira. Quite possibly this danger to the church involved not only a spiritual compromise with paganism but also the literal question of Christians’ attending actual feasts, such as the trade-guild banquets with their idolatrous aspects and their probable tendencies to immorality. Certain it is that such problems had been real in Paul’s day (Acts 15:20; 1 Corinthians 8; 10:20-28), and that the trade guilds, so necessary to the prosperity of the Christian craftsmen, were particularly numerous and important in Thyatira.”

LeRoy E. Froom, Prophetic Faith of our Fathers, Vol. 1, p. 93.

Philadelphia is the sixth of the seven churches addressed in Revelation. (The Letters to the Seven Churches, pg. 14).

“Philadelphia: A city of ancient Lydia in Asia Minor on the Cogamus River, 105 miles from Smyrna. It stood upon a terrace 650 ft. above the sea. Behind it are the volcanic cliffs to which the Turks have given the name of Devitt, or ‘inkwells’; on the other side of the city the land is exceedingly fertile, and there was produced a wine of whose excellence the celebrated Roman poet Virgil wrote. Philadelphia is not so ancient as many of the other cities of Asia Minor, for it was founded after 189 bc on one of the highways which led to the interior. … it sometimes bore the title of  ‘Little Athens’ because of the magnificence of the temples and other public buildings which adorned it. Philadelphia quickly became an important and wealthy trade center, for as the coast cities declined, it grew in power, and retained its importance even until late Byzantine times.”

“Philadelphia,” International Standard Bible Encyclopedia.