Rev. 6:9-11 (ESV)
When he opened the fifth seal, I saw under the altar the souls of those who had been slain for the word of God and for the witness they had borne.  They cried out with a loud voice, "O Sovereign Lord, holy and true, how long before you will judge and avenge our blood on those who dwell on the earth?"  Then they were each given a white robe and told to rest a little longer, until the number of their fellow servants and their brothers should be complete, who were to be killed as they themselves had been.
Genesis 15:16 (ESV)
And they shall come back here in the fourth generation, for the iniquity of the Amorites is not yet complete."
People often chafe at all the war in the Old Testament.
I find that peculiar. They hold it against God. Yet if it wasn’t for the Old Testament and God’s revelation in general permeating the culture in which we live it is doubtful that they would see peace as such a great virtue.
In any case though they do chafe at it, they can’t see how it is a loving God could declare genocide as he did when the fourth generation returned to Canaan. I say wait until this world’s sin is complete and not just the sins of the Amorites.
God was patient in the Old Testament and his people suffered as they waited for justice to be meted out upon the Amorites. Meanwhile the Amorites continued filling the land with blood, offering child sacrifice and so on. When their iniquity was complete, God’s patience finally tested, then God sent in the Israelites.
“then they were each given a white robe and told to rest a little longer, until the number of their fellow servants and their brothers should be complete, who were to be killed as they themselves had been.”
“Should be complete” Only God knows when that will be. In the meantime we suffer here in this world. Though most of the time I can hardly consider it suffering. There is an element to it though. And when one part of the body hurts we all hurt with it. The number it seems is not yet complete. God exercises patience with the world as the world persecutes his church, kills his saints. Those saints rest. They rest as they wait for the rest of us to join them. We need not worry about them. Eventually God will, Jesus will, avenge the blood of those who have been killed.
Yes there shall be rejoicing when their blood is avenged. The time to mourn is now. They are our brothers and sisters who persecute us. They are our brothers and sisters for whom Christ died. Yet they persecute Christ. It is not pleasant to think of what will happen to them. But on the last day as the blood of the Martyrs is avenged, as justice is served to this world we will rejoice if for nothing else for having escaped the judgment ourselves. But then also for seeing justice.