Jesus called Peter a "Rock" long before Peter was stable and mature. God calls out our potential versus our failure for He knows that our failures do not define who we are, nor who we are going to become.
I struggle with the idea of the "bigger picture" and wanting to know what it is. I struggle with focusing on my failures versus my successes. Sometimes, all I can see our the failures, and once I see one time I made a mistake, it out shines all the times I did something right, something good.
God is into being creative and unique. Just think, every person has different finger prints, DNA, laughs, and so much more. Much like snow flakes, no two people are alike. God created the one and only "you" and never will there be anyone prepared for exactly what God has prepared you for. You cannot let your past failures, the opinions of others, or even the devil devalue who you are as a person.
Do not let others tell you that you have no worth, aren't stable enough, aren't good enough, pretty enough, smart enough, funny enough, or more. If someone tells you this, they are lying to you. Your value is not determined by what you have been through.
Take a $20 bill or example. That $20 bill has probably been through more than anyone can imagine. It has probably been trampled, rained on, used as a coaster, used for other things, and so much more, but when it comes down to it, it's value didn't decrease because of what it had been through, right? Just like your value doesn't decrease because of what you have been through.
Your past is not a problem for God. Your past does not disqualify you from the love of God, or from reaching your potential. Just remember, your value doesn't decrease because of what you have been through, it gives you character and a story to tell. Also, your value doesn't decrease because someone said it does. Your value is in God, not those around you.
We are rocks, just like Peter.