The Epistle From Patmos

Of all of the twelve apostles, only John survived to old age (which doesn't mean that he wasn't martyred then; see Martyrs). John's long life wasn't just some sort of favoritism, it was a matter of him being given the responsibilities for things that required him to remain alive. The first was to care for Mary, the mother of Jesus, through to the end of her natural life:

"^19:26 When Jesus therefore saw his mother, and the disciple standing by, whom he loved, he saith unto his mother, Woman, behold thy son! ^19:27 Then saith he to the disciple, Behold thy mother! And from that hour that disciple took her unto his own home.

^19:28 After this, Jesus knowing that all things were now accomplished, that the scripture might be fulfilled, saith, I thirst. ^19:29 Now there was set a vessel full of Vinegar: and they filled a sponge with vinegar, and put it upon hyssop, and put it to his mouth.

^19:30 When Jesus therefore had received the vinegar, he said, It is finished: and he bowed his head, and gave up the ghost [see Giving Up The Ghost]" (John 19:26-30 KJV)

"Write in a book and send it unto the seven churches which are in Asia"

The age difference between Mary and her nephew John (see Aunt Mary?) was likely less than twenty years. Since we know that the book of Revelation was written around 90 AD, about sixty years after Christ's crucifixion, Mary likely lived to be quite old. There was no other reason to protect John for that long; he could have been given to write the apocalypse (see the Fact Finder question below to understand the meaning of apocalypse and revelation) anytime sooner.

When the time came that John was held as a prisoner by the Romans (indicating that John was nearing the end of his ministry and perhaps his execution) on the island of Patmos (located off the west coast of Turkey - see the map), John was given to write Revelation, which, although regarded as a book of Prophecy (which it is), was originally an epistle (most of the other Epistles also were composed of prophecy), a book-length letter, to the "seven churches of Asia," given to John by a vision of Christ.

"^1:9 I John, who also am your brother, and companion in tribulation [see Trials and Tribulations], 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. ^1:10 I was in the Spirit on the Lord's day, and heard behind me a great voice, as of a trumpet, ^1:11 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.

^1:12 And I turned to see the voice that spake with me. And being turned, I saw seven golden candlesticks; ^1:13 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. ^1:14 His head and his hairs were white like wool, as white as snow; and his eyes were as a flame of fire; ^1:15 And his feet like unto fine brass, as if they burned in a furnace; and his voice as the sound of many waters. ^1:16 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.

^1:17 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: ^1:18 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.

^1:19 Write the things which thou hast seen, and the things which are, and the things which shall be hereafter; ^1:20 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." (Revelation 1:9-11 KJV)

Fact Finder: Why is the book of Revelation also known as the Apocalypse?
See Apocalypse