He that hath an ear - See the notes on Revelation 2:7.
The Epistle to the Church in Philadelphia
This epistle Revelation 3:7-13 comprises the following subjects:
(1) The usual address to the angel of the church, Revelation 3:7.
(2) the reference to some attribute or characteristic of the speaker, Revelation 3:7. He here addresses the church as one who is holy and true; as he who has the key of David, and who can shut and no one can open, and open and no one can shut. The representation is that of one who occupies a royal palace, and who can admit or exclude anyone whom he pleases. The reference to such a palace is continued through the epistle.
(3) the usual declaration that he knows their works, and that he has found that they had strength, though but a little, and had kept his word, Revelation 3:8.
(4) a declaration that he would constrain some who professed that they were Jews, but who were of the synagogue of Satan, to come and humble themselves before them, Revelation 3:9.
(5) the particular promise to that church. He would keep them in the hour of temptation that was coming to try all that dwelt upon the earth, Revelation 3:10.
(6) the command addressed to them as to the other churches. He solemnly enjoins it on them to see that no one should take their crown, or deprive them of the reward which he would give to his faithful followers, Revelation 3:11.
(7) a general promise, in view of the circumstances in Philadelphia, to all who should overcome, Revelation 3:12. They would be made a pillar in the temple of God, and go no more out. They would have written on themselves the name of his God, and the name of the holy city - showing that they were inhabitants of the heavenly world.
(8) the usual call on all to attend to what was said to the churches, Revelation 3:13.
Philadelphia stood about 25 miles south-cast from Sardis, in the plain of Hermus, and about midway between the river of that name and the termination of Mount Tmolus. It was the second city in Lydia, and was built by King Attalus Philadelphus, from whom it received its name. In the year 133 b.c. the place passed, with the country in the vicinity, under the dominion of the Romans. The site is reported by Strabo to be liable to earthquakes, but it continued to be a place of importance down to the Byzantine age; and, of all the towns in Asia Minor, it withstood the Turks the longest. It was taken by Bajazat, 1392 a.d. "It still exists as a Turkish town, under the name of Allah Shehr, 'City of God,' that is, the 'High Town.' It covers a considerable extent of ground, running up the slopes of four hills, or rather of one hill with four flat summits. The country, as viewed from these hills, is extremely magnificent - gardens and vineyards lying at the back and sides of the town, and before it one of the most beautiful and extensive plains of Asia. The missionaries Fisk and Parsons were informed by the Greek bishop that the town contained 3,000 houses, of which he assigned 250 to the Greeks, and the rest to the Turks (the mid-19th century). On the same authority it is stated that there are five churches in the town, besides twenty others which were too old or too small for use. Six minarets, indicating as many mosques, are seen in the town, and one of these mosques is believed by the native Christians to have been the church in which assembled the primitive Christians addressed in the Apocalypse. There are few ruins; but in one part are four pillars, which are supposed to have been columns of a church.
One solitary pillar has been often noticed, as reminding beholders of the remarkable words in the Apocalypse - 'Him that overcometh I will make a pillar in the temple of my God'" (Kitto's Encyclopedia. See also the Missionary Herald for 1821, p. 253; 1839, pp. 210-212). The town is the seat of a Greek archbishop, with about twenty inferior clergy. The streets are narrow, and are described as remarkably filthy. The engraving in this volume will give a representation of the town as it now appears.

He that hath an ear - The usual caution and counsel carefully to attend to the things spoken to the members of that Church, in which every reader is more or less interested.
Epistle to the Church at Philadelphia

He that hath an ear, let him hear,.... See Gill on Revelation 2:7.

(See on Revelation 2:7.)