It's also a quote from the Gemara, and it crops up in a whole lot of places whenever you get into a discussion about why apparently 'bad' things can happen to apparently 'good' people.
This idea underpins the basic fundamentals of living life with emuna, as set out by Rav Arush, namely:
1) God is doing everything in the world.
2) Everything that happens to me is for my good, even the stuff that's hurting me and is very painful and incomprehensible.
3) God is using the event, incident, occurrence or suffering to send me a message that I need to work on something, fix something, or change in some way.
Now, there are many flavours of heresy in the Jewish world, but one of the most popular, particularly in frum circles, is the idea that God sends people suffering stam, for absolutely no good reason.
The basic complaint goes like this:
"I'm a kosher person; I keep tons of mitzvoth; I pray with a netz (sunrise) minyan every day; I stopped watching Superman movies 20 years' ago; I've made a number of sacrifices to keep Hashem's torah, ergo - I don't deserve any of this hard, horrible stuff that's happening to me."
It sounds pretty convincing, doesn't it?
Until you remember one thing: there is no suffering without prior sin.
If someone is being sent a difficult or hardship, it's ALWAYS for a good reason.
The 'sin' in question is sometimes leftover from a previous lifetime
Here's where we hit a very necessary and often overlooked point of clarification: sometimes, the issue you need to fix in your soul is left over from a previous lifetime. It could well be that in this lifetime you are Miriam the super-pious light of the world, but in a previous lifetime, you may well have been Jack the Ripper - and that's a spiritual debt that still needs paying down.
So you get sent a whole bunch of very difficult trials that really, Miriam the super-pious light of the world doesn't deserve, but that are still a deep discount for Jack The Ripper.
This is where a person gets to really live their emuna, and this is often the whole test, and the whole 'sin' that needs fixing: are you going to see God behind everything that's happening to you, and to acknowledge that He's doing it all for your eternal good, and to get the message that you need to do some super-human work on your emuna?
Or are you going to complain, feel sorry for yourself, and convince yourself that you're already perfect, and God must have made some big mistake so start picking on you so unfairly?
The rule is this: If you're alive, you still have work to do.
If you're still alive, no matter how 'perfect' you think you are, there are still bad character traits to fix, mistakes to rectify, and levels of emuna to work on achieving. The process of self-improvement only ends when we die.
In his book Words of Faith, Rav Levi Yitzhak Bender puts it like this:
"Know yourself! Even if the entire world says that you are righteous, you have to know who you are…When a person truly knows himself, it is not possible that he shall not mend his ways…But when he deceives himself and imagines that he is something - why should he work to get better?"
On a personal note, a few months' ago I went through a period of extreme difficulties and very hard tests in emuna. Initially, I couldn't understand why God was sending me all this hard stuff. I mean, I'd sacrificed so much for my frum lifestyle, I spoke to God for an hour every single day, I was continually working on myself.
My underlying attitude was: "You've got the wrong gal, Hashem! Stop sending me all these undeserved difficulties and go pick on someone else!!"
It took me many, many months of working things through, and at least one trip to Uman, but finally I realised that God really had sent me exactly what I was due - and had probably even giving me a huge discount on what I could have had coming to me.
I was so full of arrogance and pride about all my religious 'accomplishments', that I hadn't realised just how flawed and occasionally nasty I still actually was (especially to my husband and kids…)
I was completely fooling myself as to my true level, and God didn't want that state of affairs to continue any longer.
There really was 'no suffering without prior sin', even though it didn't look like that to me, or others, at the time.
God is just. He's righteous. He only sends us what we need to do the work of fixing our souls for eternity. And if we don't believe that, than however 'pious' and 'perfect' we may think we are, we still have an awful lot of spiritual work to do.