Rather than mitigating the apocalyptic tone, the New Testament actually amplifies the idea that God will conclude this age with fire. 

The Gospels introduce John the Baptist warning the people of Israel about “the wrath to come” (Luke 3:7), with the unrepentant being “thrown into the fire” (v. 9) and the Messiah coming to “burn up the chaff with unquenchable fire” (v. 17, nasb; cf. Isa. 66:24). Jesus likewise warns the crowds concerning “that day” (Matt. 7:22): “Every tree that does not bear good fruit is cut down and thrown into the fire” (v. 19). And later he declares, “Just as the weeds are gathered and burned with fire, so will it be at the end of the age” (Matt. 13:40). Similarly, Jesus uses the metaphor of a vine and branches to communicate the fearful apocalyptic reality: “If anyone does not abide in me he is thrown away like a branch and withers; and the branches are gathered, thrown into the fire, and burned” (John 15:6).  - John P. Harrigan, The Gospel of Christ Crucified, p.68