These believers had died for their faith, and the wrong done to them had not yet been set right. Their question is the cry of people waiting on God's justice. They do not take revenge themselves; they bring their cause to God. Gill says they desire it "not out of any sinful or malicious affection, but that the holiness and justice of God might appear." Gill explains that they appeal to Him as "holy," who cannot but hate the evil done to them, and "true," faithful to His word.

The answer comes first as a gift: "white robes were given unto every one of them" (Revelation 6:11). Then with a word: "they should rest yet for a little season, until their fellowservants also and their brethren, that should be killed as they were, should be fulfilled." They are not told the day, but they are told to rest, and that God's timing has a purpose. Later in the book, heaven praises God because He "hath avenged the blood of his servants" (Revelation 19:2).

The altar recalls the temple, where sacrifices were offered and prayers rose to God. Barnes admits the reason "is not so apparent," but suggests two probable reasons: the altar was where sin was atoned for, and it was the usual place of prayer. He also calls this passage "one of the incidental proofs in the Bible that the soul does not cease to exist at death."

The word "Lord" here is the Greek despotes, which Thayer's lexicon defines as "a master, lord." It is the source of the ESV's "Sovereign Lord." It is used of God in prayer only a few times in the New Testament, including Luke 2:29 and Acts 4:24. Gill notes that the One addressed may be either the Lamb in the midst of the throne or God the Father who sat upon the throne. He also says the white robes were given "as a token of their innocence," since they did not die for any crime.

This question shows that God's people may bring their deepest wrongs to Him and ask Him how long. Heaven does not rebuke the martyrs for asking. They are given robes and rest. Barnes describes them as still conscious, "engaged in prayer," and "manifesting earnest desires for the divine interposition to avenge the wrongs which they had suffered." Matthew Henry reminds us what persecutors cannot do: "Persecutors can only kill the body, and after that there is no more that they can do; their souls live."

The cry "How long" echoes the prayers of God's people in the Psalms and Prophets (Psalm 13:1; Habakkuk 1:2). Here it rises from heaven itself. God's answer is not never but "a little season." Justice is certain, and His timing includes others who will still be faithful (Revelation 6:11).