The apostle John tells why these saints suffered martyrdom: "for the word of God and for the testimony which they held." For John, these two are important elements, and they occur several times in Revelation. In opening the book, the apostle contends that he himself "bore witness to the word of God, and to the testimony of Jesus Christ" in Revelation 1:2, and in verse 9 he says he "was on the island that is called Patmos for the word of God and for the testimony of Jesus Christ." Later, when observing a vision of God's people contending with Satan, he writes, "And they overcame him by the blood of the Lamb and by the word of their testimony, and they did not love their lives to the death" (Revelation 12:11). A statement similar to Revelation 6:9 appears in Revelation 20:4: "And I saw the souls of those who had been beheaded for their witness to Jesus and for the word of God."
The first element, the word of God, is straightforward: It is the truth, the inspired revelation of God, that we find today in the Bible. For John and many in the first century, it was the Old Testament combined with the life and teachings of Jesus Christ. Only later was this supplemented by the epistles of the apostles, Acts, and Revelation. (No one can be certain when the authoritative canon was compiled, but all the components were likely in place by the time John died. Using Isaiah 8:16, some believe that he authorized the present canon before his death, c. AD 100.) Unlike many today, these martyrs of the fifth seal do not take God's Word for granted, believing that its message is personally vital, current, and authoritative, and they are willing to die rather than compromise with its instruction.
The second element, the testimony which they held, can seem to some to be more complex. The key word, testimony, is the Greek word marturían, which means either "the act or office of testifying" or "what one testifies." In modern terms, it is either the giving of evidence, as before a judge in a courtroom, or the evidence itself. The word witness is similarly used, as, for instance, the Two Witnesses of Revelation 11 are called mártusín ("witnesses" or "martyrs"), a related word. Their "testimony," then, is evidence they give or a witness they provide.
We should not forget the final phrase, "which they held," as it adds definition and emphasis to their testimony. The evidence they give means something special to them! It is not as if they witnessed an auto accident and, as unbiased bystanders, simply testified about how it happened. Their testimony is something so precious that they hold it fast, bear it, maintain it, keep it in trust, possess it, consider it, believe it, and adhere to it.
How do they give their testimony? It could be different for each one, but notice Jesus' interpretation of this seal in Luke 21:12-19:
But before all these things [the heavenly signs of the sixth seal], they will lay their hands on you and persecute you, delivering you up to the synagogues and prisons, and you will be brought before kings and rulers for My name's sake. But it will turn out for you as an occasion for testimony. Therefore settle it in your hearts not to meditate beforehand on what you will answer; for I will give you a mouth and wisdom which all your adversaries will not be able to contradict or resist. You will be betrayed even by parents and brothers, relatives and friends; and they will send some of you to your death. And you will be hated by all for My name's sake. But not a hair of your head shall be lost. In your patience possess your souls.
He specifically mentions testifying before religious authorities, in prisons, and before secular leaders. These are the "classic" occasions for witnessing of the truth, all of which are reported as happening to the apostles in the book of Acts. He also hints at other ways of testifying, more personal ones that involve relatives and "friends" seeing a Christian practicing his beliefs or hearing him propounding the truth, and betraying him to the authorities.
Hebrews 11 gives multiple examples of the heroes of faith making a witness of the true God and His way. Abel, for example, bore witness by making an acceptable sacrifice (verse 4). Enoch's translation was witness that He pleased God (verse 5). Noah's obedience in constructing the ark bore witness of his faith (verse 7). Abraham testified of his allegiance in many ways: leaving Ur (verse 8), dwelling in tents in Canaan (verse 9), and sacrificing Isaac (verse 17). Sarah, too, testified by conceiving and bearing the promised son, Isaac (verse 11). Later, Moses showed his faith by refusing royal rank (verse 24), forsaking Egypt (verse 27), and keeping the Passover (verse 28).
Likewise, we give testimony of our devotion to God and our beliefs in simple, everyday acts, many of which we probably never consider to be witnessing. We make a witness to other members of our families with our every word, act, and decision. We witness of our adherence to law in our public activities, from driving our cars to paying our taxes. Our diligence and thoroughness on the job testify of our godly character or lack thereof. One could go so far as to say that everything we say and do that is witnessed by others shouts out the testimony that we hold.
Are we, like these martyred saints, willing to lay down our lives for God's Word and our beliefs? It may never come to that for any of us personally, but do we have the sacrificial attitude applauded by Revelation 6:11 and many other New Testament verses? Do we value God's revelation of His way of life highly enough to defend it despite the cost? Do we, as Jesus warns in Luke 14:26, "hate" our lives enough to be His disciples?