Once the prodigal son came to himself, and took a survey of his own condition, he was quickly brought to acknowledge his unworthiness. He remembered how he got into his current condition. His heart longed to know the mercy of God upon his sinfulness. This is the key to repentance that results in been born again, and knowing the mercy and forgiveness of our Heavenly Father.
When we come to know just how we have denied a holy God is right into our lives we quickly are humbled and turn to Him for forgiveness.
What we learn about our selves, it would make us rely only on free grace, when we consider how much God requires, and how little we perform. We would say with David in Psalms 71:16 “I will go in the strength of the LORD, I will make mention of thy righteousness, of thine only. “