Revelation 4:1 After these things I looked, and behold, a door standing open in heaven. And the first voice which I heard was like a trumpet speaking with me, saying, “Come up here, and I will show you things which must take place after this.”

It is my opinion John experienced the still future event of the rapture.
Although he could not experience the actual event since it has not happened. But then most of Revelation has not happened.
So far he saw the entire church age up to the point of the catching up of God’s people.
A door opened in heaven and a door does not open unless someone is going to go through it one way or the other.
John is the one invited in by a voice sounding like a trumpet.
1 Thess 4:16 For the Lord Himself will descend from heaven with a shout, with the voice of an archangel, and with the trumpet of God.
1 Cor 15:52 in a moment, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised incorruptible, and we shall be changed.
Things change after this verse.
One thing said several times throughout chapters two and three is the phrase “He who has an ear, let him hear what the Spirit says to the churches.”
The church is not mentioned again until the very end of Revelation, in chapter 22.
From this point forward, Revelation becomes a Jewish book. Its imagery, the two witnesses, the salvation of 144,000 all deal with Israel and not the church.