After this I looked, and there before me was a door standing open in heaven. And the voice I had first heard speaking to me like a trumpet said, “Come up here, and I will show you what must take place after this.” (Revelation 4:1 NIV)
In this verse we see that the Apostle John was given the opportunity to ascend to heaven in a vision to see the future from a celestial viewpoint. The voice inviting him to heaven here is probably the same voice that he heard back in Revelation 1:10, which is obviously the voice of Jesus Himself.
The question arises: what did John really see? Did He really go to heaven and witness God in all His glory?
The answer is “no” in the sense that this vision did not get to experience heaven the way that the angels and Jesus and the resurrected saints experience it. He did not see a full manifestation of God, because such a manifestation would have killed him (Exodus 33:20). In fact John Himself admits that no human, other than Jesus who is fully God and fully man, has ever seen God (John 1:18).
So what John experienced was probably not a full manifestation of the scene in heaven, but a representation of it that was symbolized in a way that mortals like Him and us could understand. But I want to be clear that I am not saying that His vision was not real! It was extremely real. It was a message from God to man, which we would do well to heed. The things that are revealed in this vision are given in plain terms that are easy to understand. These events predicted in this vision will really happen one day, for, as Jesus said, they “must take place after this.”
So we need to take this revelation seriously!