Asking Job whom he thinks he is to even think of asking that question. Not everyone is happy with that answer. So, some have tried to reason out if God could even exist if sin exists. And what we come up with is that it cannot be reasoned that God does not exist just because sin does. Now, I have been using interchanging the words sin and suffering as if they have the same meaning.
Sin is that which causes suffering.
But this suffering caused by sin can at times, if truly understood, bring about something wonderful. The revelation, comprehension, of our purpose is only possible by the Grace of the God who created us. Grace renews our human purpose despite our human sin. We can see that Grace stems from creation itself. His love for his creation is so great that it is felt as Grace despite the great separation that sin has cause in the lives of every person.