When the lamb opened the fifth seal,

I [John] saw under the altar the souls of those who had been slaughtered because of God’s word and the testimony they had given about him.  

       They cried out in a loud voice, “Holy and true Master, how long before you judge and take revenge on those living on earth who shed our blood?”  

            Each of the souls was given a white robe. They were told to rest a little longer until all their coworkers, the other Christians, would be killed as they had been killed.