The fourth chapter of Revelation is the beginning of a vision in the throne-room of heaven. John indeed uses the language of vision, which does not suggest that he has been actually transported into heaven itself. It is more than a mental image, but neither is it a change of location.
The vision of the creatures in heaven is obviously rooted in the context of the Old Testament-- Ezekiel and Isaiah. The identity of the twenty-four elders bowing in worship has been debated. It can represent an angelic order in heaven that compliments the twenty-four priestly and levitical orders of 1 Chronicles (24:4; 25:9-13). Others suggest that the twenty-four elders represent the whole people of God as represented by the twelve tribes of Israel and the twelve apostles, who signified Jesus' intention to reconstitute the people of God in his ministry.
The scene in Revelation 4 clearly is one of power and majesty. God is on his throne and in charge. The God of Israel is not a pretender deity demanding worship from his subjects; this God is worthy of worship because he is indeed God. At the beginning of John's apocalyptic vision, his hearers are comforted by the worship of God in the heavenly court. In the midst of trials and tribulations they are reminded that those who oppress them will face justice in God's appointed time. In verse 11 the twenty-four elders shout in worship, "You are worthy, our Lord and God, to receive glory and honour and power." The Roman historian Suetonius tells us that this was essentially the same greeting given by Roman subjects to the Emperor Domitian as he arrived in triumphant procession. The message at the end of chapter four is too obvious to be missed. Only the one true God is worthy of such honor and glory. Domitian's divine pretensions are blasphemous.