I don't see the rest of Rev.1, so I feel led to provide it here.
Rev 1:9-20
9 I John, who also am your brother, and companion in tribulation, and in the kingdom and patience of Jesus Christ, was in the isle that is called Patmos, for the word of God, and for the testimony of Jesus Christ.
John declares his relationship with those he was given to write our Lord's Revelation down to, the seven Churches in Asia Minor. John was being held captive on the Isle of Patmos when Christ gave Him His Revelation to send to the Churches. So this is about Testimony of Jesus Christ given through... John, His Apostle.
10 I was in the Spirit on the Lord's day, and heard behind me a great voice, as of a trumpet,
John had just spoke of Christ's future coming back in the 7th verse, linking the subject of this verse with it. It's about the final trumpet, the 7th, the "last trumpet" and "trump of God" which Apostle Paul also spoke of that will occur on "the day of The Lord". John hearing that "great voice, as of a trumpet" points back to the "great shout" of 1 Thess.4:16 and John 5:28-29. This event of a great trumpet sounding at the end was first given in prophecy like Isa.27:13 and Zech.9:14.
11 Saying, I am Alpha and Omega, the first and the last: and, What thou seest, write in a book, and send it unto the seven churches which are in Asia; unto Ephesus, and unto Smyrna, and unto Pergamos, and unto Thyatira, and unto Sardis, and unto Philadelphia, and unto Laodicea.
The Alpha and Omega is a type expression God first used in the OT Books of Isa.41:4, where He said of Himself, "I The LORD, the first, and with the last, I AM HE." (See also Isa.44:6; 48:12 where He proclaims this expression also.) By this type of expression, Christ Jesus is proclaiming He is The God of The Old Testament. Alpha and Omega are the first and last letters of the Greek alphabet. The expression is symbolic of completeness, eternal.
John is told by Christ Jesus to write down what he sees in a book, and send it to the seven Churches in Asia. These were physical locations in Asia Minor. They were real existing Churches in John's days. And they all represent seven 'types' of Churches to be found all the way to the end of this world.
12 And I turned to see the voice that spake with me. And being turned, I saw seven golden candlesticks;
13 And in the midst of the seven candlesticks one like unto the Son of man, clothed with a garment down to the foot, and girt about the paps with a golden girdle.
In The Spirit, John turns to see Who spoke to him, and he sees seven golden candlesticks. John will be later told what these seven golden candlesticks represent in the Heavenly. In the midst of the candlesticks stood "the Son of man", an expression for our Lord Jesus Christ. John then begins to describe how He was manifest to him.
14 His head and His hairs were white like wool, as white as snow; and His eyes were as a flame of fire;
15 And His feet like unto fine brass, as if they burned in a furnace; and His voice as the sound of many waters.
16 And He had in His right hand seven stars: and out of His mouth went a sharp twoedged sword: and His countenance was as the sun shineth in his strength.
In this description is a parallel to God's Presence Whom Daniel saw in Dan.7:9 and Dan.10:6, and Ezekiel in Ezek.8:2. This is our Lord Jesus Whom John saw.
17 And when I saw Him, I fell at His feet as dead. And He laid his right hand upon me, saying unto me, "Fear not; I am the first and the last:"
18 I am He That liveth, and was dead; and, behold, I am alive for evermore, Amen; and have the keys of hell and of death.
No doubt now that John was seeing our Lord Jesus Christ Who died on the cross but was raised from the dead to the right hand of The Father. These "keys" are symbolic for His Salvation, the door which He opens for those of Faith, but closes upon those who refuse that Faith (Matt.25).
19 Write the things which thou hast seen, and the things which are, and the things which shall be hereafter;
Christ commands John to write down what he "hast seen" (past), and things "which are" (present), and things "which shall be hereafter" (future). So as just about every Book of God's Word is written in this way, covering things past, present, and future, our Lord's Book of Revelation is no different.
20 The mystery of the seven stars which thou sawest in My right hand, and the seven golden candlesticks. The seven stars are the angels of the seven churches: and the seven candlesticks which thou sawest are the seven churches.
(KJV)
Oft times in God's Word, lot of prophetic Messages are not given until the latter parts of the chapter or Book. I think it serves as a type of test by our LORD, to see who's paying attention or not.
With this verse, John is told the mystery of the seven stars and seven candlesticks. The seven stars represent 'angels' over the seven Churches. And the seven candlesticks represent the seven Churches. In Rev.2, Christ warns the Church at Ephesus that if they didn't repent, He would remove their 'candlestick' out of its place. So where are those seven candlesticks? They are in Heaven, and represent a Heavenly pattern for seven Churches. This pattern was first given in Zechariah 4. This mystery is going to relate strongly to a later Message Christ gave in Revelation 11 about His two witnesses and two of the candlesticks.