Poole on Revelation 3:7: Our David, Holy and True
Verse 7: And to the angel of the church in Philadelphia write; These things saith (Acts 3:14) he that is holy, (1 John 5:20; Rev. 3:14; 1:5; 6:10; 19:11) he that is true, he that hath (Is. 22:22; Luke 1:32; Rev. 1:18) the key of David, (Matt. 16:19) he that openeth, and no man shutteth; and (Job 12:14) shutteth, and no man openeth…
[Of Philadelphia] Which is threefold, 1. one of Egypt: 2. one of Syria: 3. (concerning which it is here treated [Gomar]) one of Phrygia (Bochart’s Sacred Geography “Phaleg” 3:8:195), or of Mysia (Gomar, Camerarius, Grotius), founded by Attalus, who had the cognomen Philadelphus (Grotius), or, as it is pleasing to others, of Lydia (Gomar).
And to the angel of the church in Philadelphia write: see the notes on Revelation 1:20; 2:1. Of this Philadelphia we read no more in holy writ. We are told there were three cities of that name, one in Egypt, one in Syria, another in Phrygia, or in Mysia or Lydia, which is that here intended.
[Holy (as Christ is also called in Acts 3:14 [Grotius]; Luke 1:35; holy with respect to nature and life [Gomar]; who is the holy one of the holy ones, Daniel 9:24 [Lyra, Gomar]; the author and lover of holiness [Menochius]; who is not able not to love this holy Church [Durham]) and true] That is, Truthful and constant to His promises: or, that He has true holiness (Menochius), that is to say, extraordinarily holy. For that which excels in a category is often called true, Jeremiah 2:21; John 1:9; 4:23; 6:32; 15:1; 1 Thessalonians 1:9; 1 Peter 5:12; 1 John 2:8. He says this so that the Bishops might imitate His holiness as far as that can be done (Grotius); or, so that to the Bishop of Philadelphia, who was of little virtue, He might set forth His own perfect holiness, a mirror and goal, as it were, so that he might aspire and stretch toward it (Menochius).
These things saith he that is holy; that is, the Holy One, Acts 3:14. He that is true; true to his word of promise or threatening.
[Who hath the key of David] Thus He speaks, either because Christ was born from the shoot of David: or, because David prophesied many things concerning Christ (Pererius). The key of David, by an Ellipsis for the key of the house of David (Drusius’ Of Sacred Observations 16:17, similarly Glassius), as it is fully express in Isaiah 22:22 (Gomar). Thus Micah 4:2, the mountain of the Lord, that is, the mountain of the house of the Lord, as it is in verse 1 (Glassius’ “Grammar” 3:1:39, Drusius’ Of Sacred Observations 16:17). Thus, he went to Pompey, that is, unto the house of Pompey (Drusius). Ad Opis, unto of Ops, ad Pollucis, unto of Pollux, that is, the shrine; εἰς διδασκάλου, unto of the instructor, that is, οἰκίαν, the house (Glassius). Now, by house of David, over which Eliakim is in charge, they understand, either, his house and royal court (certain interpreters in Pererius). Or, 2. the temple of God (Pererius out of the Hebrews and Jerome, etc., Ribera), which, although built by Solomon, is rightly called the house of David, for he was the first who considered building it and decided to do so; and he left the form of it to Solomon with the material of wood, silver and gold, 1 Chronicles 28, 29 (Ribera, thus Pererius). Moreover, the house of David is the Church (Pareus, similarly Drusius, Piscator, Beza, Durham, Ribera, Pererius). A key signifies two things in Scripture, 1. the knowledge of hidden things, as in Luke 11:52 (Pererius), so that the sense might be that from Christ is the true and right understanding of the mysteries that lie in the Sacred Scripture, especially in the Psalms of David (certain interpreters in Pererius). Or, 2. some eminent power of doing something, as in Isaiah 22:22; Matthew 16:19; Revelation 1:18; 9:1; 20:1, so that it might signify David’s (some interpreters in Pererius), and therefore Christ’s, whom David wonderfully prefigured, royal power (Pererius, thus Camerarius, Zegers); so that the sense is that Christ has consummate and absolute power in the Church (Pererius, similarly Ribera, Lapide, Gomar, Pareus, Piscator), both while it is militant on earth, and triumphant in the heavens (Gomar, Piscator); of opening to whom He will, and of closing (Pererius), that is, of receiving and excluding (Gomar). [The sense:] He who not only has the prerogative of Death and Hell, as in Revelation 1:18, but the fullest authority in the house of God, just like Eliakim in the house of Hezekiah, who was of the posterity of David. This Eliakim was, as the Constantinopolitans were saying, κουροπαλάτης, the kouropalates, of Hezekiah, whose emblem of function was the figure of a key woven into his Epomidios. See Isaiah 22:22 (Grotius).
[Who, etc., ὁ ἀνοίγων καὶ οὐδεὶς κλείσει, etc.] This is clearly a Hebraic expression, in the place of which the Greeks say, οὗ ἀνοίγοντος οὐδεὶς κλείει, etc., with whom opening no one shutteth, etc. [The sense:] No one in the Palace dares to contradict Him or to act against His laws; all things are subject to Him (Grotius). Who openeth (namely, heaven to the elect [Piscator, similarly Gomar, Pareus]: who admits into His Church [Pererius, similarly Gomar, Ribera, Pareus], by giving faith and grace to them [Pererius, similarly Ribera]) and no one shutteth (that is, prevents from entering [Pareus]: that is, Those whom He admits enter [Ribera]: that is to say, Whom He leads to the Church, no one is able to shut out [Menochius]), He shutteth (to those whom He leaves in their own impiety and blindness [Pererius]: He closes heaven to reprobates [Piscator]) and no one openeth. That is, To whom He shuts the gates because of unbelief, they will not be able to enter (Ribera, Menochius). Those whom He does not choose, call, draw, will never enter. Another argument for the Divinity of Christ (Piscator).
He that hath the key of David; that is, the key of the house of David, mentioned Isaiah 22:22; the key of the church, which answered the temple, the house David designed for God: the use of the key is to open and shut, or make fast. He that openeth, and no man shutteth; and shutteth, and no man openeth; who admits into the kingdom of heaven whom he pleaseth, and none can hinder him, and shutteth out of heaven whom he pleaseth. The house of David typified the church, the church containeth the number of those that shall be saved; Christ is here described as he who hath the sole and absolute power of saving and condemning whom he pleaseth.
 Greek: Καὶ τῷ ἀγγέλῳ τῆς ἐν Φιλαδελφείᾳ ἐκκλησίας γράψον, Τάδε λέγει ὁ ἅγιος, ὁ ἀληθινός, ὁ ἔχων τὴν κλεῖν τοῦ Δαυίδ, ὁ ἀνοίγων καὶ οὐδεὶς κλείσει, καὶ κλείων καὶ οὐδεὶς ἀνοίξει.  Daniel 9:24: “Seventy weeks are determined upon thy people and upon thy holy city, to finish the transgression, and to make an end of sins, and to make reconciliation for iniquity, and to bring in everlasting righteousness, and to seal up the vision and prophecy, and to anoint the most Holy (קֹ֥דֶשׁ קָֽדָשִֽׁים׃, the holy one of the holy ones).”  Jeremiah 2:21: “Yet I had planted thee a noble vine, wholly a right seed (זֶ֣רַע אֱמֶ֑ת, a true seed): how then art thou turned into the degenerate plant of a strange vine unto me?”  See, for example, Isaiah 11:1, 10; Jeremiah 23:5.  Observationum Sacrarum.  Cicero’s Epistles to Pomponius 11:9.  In Greek mythology, Ops was the mother of Jupiter, the goddess of abundance; her temple was located in Rome. Castor and Pollux were twin sons of Leda, but they had different fathers, Tyndareus (a mortal) and Zeus respectively. When Castor died, Pollux asked Zeus to allow him to share his immortality with his brother; Zeus granted the request and they were transformed into the Gemini constellation. The Temple of Castor and Pollux was built in the fifth century BC in Rome.  Isaiah 22:20.  The Kouropalates was in charge of the running of the palace.  Epomidios here appears to refer to some sort of garment worn on the shoulder, from the Greek adjective ἐπωμίδιος, on the shoulder.  The Textus Receptus reads κλείει, in the present tense.