What does the Bible say about martyrs?

In Revelation 6:9-10, the souls of martyrs are seen under the altar, crying out for God to avenge their blood shed for the Word of God and their testimony. These martyrs represent believers who prioritize their faith even to the point of death, declaring the preciousness of God's Word to them. Their blood symbolizes a sacrificial offering before God, reminiscent of the sacrifices in the Old Testament, where the life was in the blood (Leviticus 17:11). This shows that though they were killed by men, they find rest and vindication in God's sovereignty and promise of justice.