I believe one of the things that is missed by many Bible students who study the Apocalypse is that John is given a vision of the Temple of God and what occurs therein. For example, the first chapter revealed Jesus standing among seven golden lampstands (Revelation 1:12-13). The single lampstand with seven branches, upon each of which were seven lamps, stood in the Holy Place, or the first room of Solomon’s Temple, and later Herod’s Temple. Before the building, itself, was a brazen sea, which answers to the sea of glass, which stood before the throne of God in heaven (cf. Revelation 4:6). Therefore, the throne room, into which John was permitted to enter at least in the Spirit (Revelation 4:1-2), would have to be the Most Holy Place. It is in this place that the Mercy Seat was placed in the ancient Jewish Temple. Without this understanding, it may be difficult to interpret what follows.
In the first few chapters of the Apocalypse, John seems to have been given a vision of the Temple of God in heaven, because, first of all, he saw seven golden lamps (Revelation 1:12), which were before the throne, which he also saw in Revelation 4:5. The throne, which John saw, was, no doubt, the Mercy Seat, upon which the writer of Hebrews says Jesus sat (Hebrews 1:3; 10:12). Therefore, the words “after (G3326) this” (Revelation 4:1) must mean John was given a vision of the Holy of Holies, because he had already witnessed in the first three chapters of the Apocalypse, what had been taking place in the Holy Place. So, after (G3326) the Holy Place was the Most Holy Place or the Holiest of All (cf. Hebrews 9:2-3). The same Greek word showing the Most Holy Palace was after (G3326) the second veil in the Holy Place (Hebrews 9:3) is also used in Revelation 4:1, where John was given the ability to see things beyond the place (or room) he was privileged to see in Revelation 1:12. 
Many people today believe “after this” (Revelation 4:1) refers to things mentioned at this point and beyond would be fulfilled in the distant future, but, if that were true, none of the near phrases of the Apocalypse would have any meaning whatsoever (cf. Revelation 1:1, 3; 22:6-7, 10, 12, 20). Moreover, all the writers of the New Testament, who predicted that the Lord’s coming would be in their expected lifetimes, would have been wrong, people such as Paul (Romans 13:11-12; Philippians 4:5), Peter (1Peter 4:5, 7; 2Peter 3:9-11) and James (James 5:8-9).
Remember, John was told to:
Write the things which thou hast seen, and the things which are, and the things which shall be hereafter; (Revelation 1:19).
That is, John was told to write what he saw, and Revelation 1:9-20 contains all “the things which (John) had seen…” The second and third chapters of the Apocalypse contain “the things which (G3739) are (G1526)” or “what (they) are.” That is, John was told to explain in Revelation 2 & 3 what he saw in Revelation 1:9-20. The third matter that John was told to write about was “the things which shall be hereafter” or, literally, “the things which come after these things.” In other words, John was told to write about the things in the next room of the Temple or record what he saw taking place in the Most Holy Place. Having recorded what he saw in the Holy Place (Revelation 1:19), John was brought into the next room – after this (Revelation 4:1), where he was immediately in the Spirit (Revelation 4:2), and was told to record what he saw here. Thus, he was permitted to see what lay beyond the opened door. This same word is used to depict the gate of the Temple courts in Acts 3:2 and again in Acts 21:30. I submit that the “open door” in Revelation 4:1 pertains to the veil removed between the door into the Most Holy Place from the Holy Place of the Temple. This is where we find John at this point in the Apocalypse.
If this understanding is logical and true, i.e. that John was in the Temple of God, then to be **in** heaven is to be **in** the Temple of God or, more specifically, to be in the Most Holy Place within the Temple of God. This also seems to indicate that the Temple at Jerusalem, which boasted of housing the Shekinah Glory or the presence of God, was, itself, considered to be heaven on earth. It was where ‘heaven and earth’ met or came together. Its model was Eden. God’s presence was in Eden, but, when Adam and Eve rebelled, they were cast out of the Garden (the Most Holy Place) and they were not permitted to reenter there. This fact points to the veil between the Most Holy Place (viz. the Garden) and the Holy Place and its courts (viz. Eden), where Adam and Eve were permitted to dwell thereafter.
This point of view does, indeed, challenges what is normally taught about the first few chapters of Revelation, but I think it fits the context of the book that presents Jesus as the true Witness (Prophet), our High Priest, and the King of kings.