Why do bad things happen?

 And Jesus answering said unto them, Suppose ye that these Galilæans were sinners above all the Galilæans, because they suffered such things? I tell you, Nay: but, except ye repent, ye shall all likewise perish. Or those eighteen, upon whom the tower in Siloam fell, and slew them, think ye that they were sinners above all men that dwelt in Jerusalem? I tell you, Nay: but, except ye repent, ye shall all likewise perish.

Luke 13:2-5

Does everything that happens only come to pass if God so wills it? If so, then, how can we understand what seems to us such injustices? This meme has been hotly debated over history.  What does Jesus offer as a response? 

In their minds, bad things happen to bad people.  That idea has been around since the time of Job. No, says Jesus, it's not that simple. If you want the truth, everyone is on the path that leads to destruction.  If you want to live, you must change your thinking, repent,and get on the way that leads to life.

We cry out for justice. We don't have a clue, though, that it is only of God's mercies that we are not all destroyed,  per Hosea. When we've seen this by revelation,  though, we can begin to move forward,  never accepting the accusation that God is somehow unjust. Rather, we can thank Him for His mercies, which endure forever.