Works are very important to the book of Revelation—seven times in chapters 2 and 3, and four or five other times in the rest of the book. Christ's concern is that His people are working.
The main purpose of the book of Revelation is not merely to give us insight into what is coming. It is also to convince the Christian that his loyalty, his devotion, his steadfastness, his suffering, and perhaps even martyrdom, is not in vain—that he is assured of a wonderful future. The reason for the stress on works is that character is not formed merely by knowing something but by knowledge combined with putting it to work until it becomes a habit. Over time, habit becomes character, and character follows the person right through the grave!
If we are not working, emphasizing loyalty to the Person of God and to His way, making every effort to overcome Satan, the world, and the self-centeredness within us, resisting with all of our being the temptations to do what is natural, carnal—if we are not expending our energy, and spending our time working out our own salvation with fear and trembling—it is very likely, then, that we are not going to have the character necessary to go through the grave. The wrong works will follow us, and we will not be prepared for the Kingdom of God.
Thus, what a person has done, that is, what he has worked on in this lifetime, follows him through the grave—either into the Lake of Fire or the Kingdom of God.
The book is designed to focus attention on what is of greatest concern to Christ for His people. He wants to ensure that they do not give up or become weary due to the great pressure of the times, and that they instead endure, persevere, and be loyal and steadfast to the very end.
His concern at this time is not preaching the gospel as a witness, but the salvation and continued growth of those He already has. The quality of the witness is directly tied to the quality of those making the witness. What good is it to have this wonderful, awesome message—the gospel of the Kingdom of God—carried by those who are poor examples of what it says? Christ's first priority is to ensure the spiritual quality of those who make the witness, and then the quality of the witness is ensured. We cannot let the cart get ahead of the horse. The one naturally follows the other. First things first.