This is a deep topic. First, God is not the author of evil [James 1:13, Ezekiel 33:10-11]. You can read through Genesis 2-3 to get a good idea of why we're separated from God in the first place. God doesn't owe us forgiveness- as Creator he has every right not to save anyone. It's out of His grace that forgiveness/reconciliation is offered. A lot of people have trouble with the idea of a God who punishes/will punish their wrongdoings, but the central message of the Bible (back to that Ezekiel reference agin) is that God saves us *because He loves us* and that we are saved not simply from our own evil, but from *His just wrath*.

How then is God a just judge, if He both promises to judge evil and refrains from punishing those who are forgiven? Their punishment is poured out on Jesus instead. That's the Gospel. He died willingly so that they can have life. If you believe, this is for you too.

According to whose sense of justice?

If you disbelieve the Abrahamic God, I then ask you, why would this be evil? What absolute set of values permits you to pass judgement on what is good or evil? If we're just all (un)happy random accidents, even actions that go against the rights of others can't be considered wholly evil. So what if something causes the suffering of humans? All of us, all of the people we know, everything the eye can see will simply vanish anyways after the heat death of the universe. So what is the absolute, unchanging and universal basis for calling something evil, allowing you to judge one's actions?

Now, if you do believe in Him, there's really no sense in trying to take our own warped sense of justice and apply it to God. He's the only one who has a complete understanding of every single thing that has happened and will happen, only He understands the reason for anything being the way it is. Try as we may, we'll never be able to see the big picture as He is able to.