OT God of Wrath vs. NT God of Mercy??

Why It Will Not Work to Pit the Old Testament God of Wrath against the New Testament God of Mercy

Don Carson:

As for the cries for vengeance, the Apocalypse provides stunning counterparts to the psalms.
“How long, Sovereign Lord, holy and true, until you judge the inhabitants of the earth and avenge our blood?” (Rev. 6:10), cry those who had been slain because of the Word of God and the testimony they had maintained.
“Give back to her [Babylon the Great] as she has given; pay her back double for what she has done. Mix her a double portion from her own cup. Giver her as much torture and grief as the glory and luxury she gave herself. In her heart she boasts, ‘I sit as a queen; I am not a widow, and I will never mourn.’ Therefore in one day her plagues will overtake her: death, mourning and famine. She will be consumed by fire, for mighty is the Lord God who judges her” (Rev. 18:6-8).
“Woe! Woe, O great city, where all those who had ships on the sea became rich through her wealth! . . . Rejoice over her, O heaven! Rejoice, saints and apostles and prophets! God has judged her for the way she treated you” (Rev. 18:19-20).
And there is much more of the same.
The factors we weighed when we considered similar Old Testament passages apply here as well. But the point to be made is that if we take seriously the eternal perspective that is laid out in the New Testament, then it simply will not do to write off the Old Testament witness as intrinsically harsher and therefore not something we need worry our heads about today.

Note especially Carson’s conclusion:

I think it is closer to the truth to say that in the coming of the Lord Jesus and the new covenant he sealed with his own blood, both the justice of God and the mercy of God appear in sharper relief than ever before, leaving us with correspondingly less excuse, and with great grounds for praise and worship.

—D. A. Carson, How Long, O Lord? Reflections on Suffering and Evil, 1st ed. (Grand Rapids: Baker, 1990), 105.