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God is merciful. Even the Bible says so
Romans 9 vs 16 "it's not of him that willeth nor of him that runneth but of God that sheweth mercy"

And He is also just.

Sure, the bible SAYS he's merciful, but then it also says he does some pretty merciless things, like torturing Job to death just to spite God's best friend, Satan.

I don't agree with you.

You don't have to. The story is right there in the bible.

That's one of the theological paradoxes: how an immutable Being changes his mind without changing Himself. As for chances, God has given us plenty of those as long as we are still alive.