Revelation 19:1-5 After this I heard what seemed to be the loud voice of a great multitude in heaven, crying out, "Hallelujah! Salvation and glory and power belong to our God, 2 for his judgments are true and just; for he has judged the great prostitute who corrupted the earth with her immorality, and has avenged on her the blood of his servants." 3 Once more they cried out, "Hallelujah! The smoke from her goes up forever and ever." 4 And the twenty-four elders and the four living creatures fell down and worshiped God who was seated on the throne, saying, "Amen. Hallelujah!" 5 And from the throne came a voice saying, "Praise our God, all you his servants, you who fear him, small and great."
God is a God justice. Though His justice is delayed, it is sure and complete. All who repented of their sins and believed the gospel rejoice when justice is accomplished, when the unrighteous world system is judged by God.
Nobody gets away with sin. Either a person accepts that Jesus paid the penalty for his/her sin by repenting and believing the gospel or a person pays his/her own penalty at the final judgment by being justly assigned a place in the Lake of Fire, a place of eternal torment.
Why is the great multitude rejoicing over the judgment of the unrighteous world system? The blood of the righteous was spilled by the people ruling and being ruled by evil. The righteous rejoice in the victory of the Lord over all evil. The righteous rejoice also because they know that Jesus suffered the payment for their sins for them by His death on the cross. God wins and believers in Jesus win. That is certainly cause for rejoicing.