" . . . And according to what they deserve I will judge them; then they shall know that I am the LORD!"
God always has the prerogative to judge "according to what [people] deserve," if He desires to do so. And sometimes God *does* judge in this way. All who will abide in hell will receive precisely what they deserve--nothing more, nothing less. But thankfully, the Lord does not *always* judge in this way.
The truth is, that *every* human being (excepting Jesus Christ) who will be in heaven *also* "deserves" God's righteous punishment (of hell fire and damnation). Instead, however, the Lord has shown mercy to them. God's judgment *was* fully poured out for their sins--but Jesus bore it for them, and they were spared. If this is not cause for praise of the merciful God, then nothing is.
[Puritan quote of the day: "God is doing a great work in the world, but God's ends are to make His people sweeter, like preserves, and preserve them for a longer time, and make them be more lasting in the world." --Christopher Love, in "The Dejected Soul's Cure"]