I don't know what weakness or sin Paul battled with from time to time. It was certain that it bothered him. He was not a slave to it, but it was something that disrupted his life. Paul even declares that it was a demon which brought on these attacks. Some say Paul battled some type of sickness and others say he battled his pride. No one knows for certain. Nonetheless, it was a battle which helped Paul see the Grace of God in a greater light. God's grace is his unmerited favor towards us. In other words, we all deserve to have a pile of rocks dropped on us because of our sin, but God has forgiven us and given us a way out.
We can live victorious lives through this wonderful grace from the perilous dealings of sin, but our flesh is still weak. As believers, what separates us from a sinner? One thing. We except the wonderful grace and life of God given to us through Jesus Christ. In other words, we recognize that we are sinners who need a rescuer. Paul did not have a chance to focus on himself and say " Look at me, Look how great I am." He became self aware of his weaknesses and how those weaknesses compared to the grace of God. God's mercy is sufficient for us all. The Law showed us how evil and corrupt sin is. It showed us the helplessness that Sin leaves us in, and how it separates us from the Love of God. Nothing we have is of ourselves. Not even our Faith. God has given it all to us. It is like waking up one day and finding out that all your bills have been paid, your work has been done, the grass has been mowed, and the errands have been completed by a mysterious person. God has done it all for us through His son Jesus. All we have to do is except His kindness. All we have to do is trust Him and allow His strength to help us turn from our wicked ways completely.
The point? God's grace is there for us when we fall. When we fall it does not mean sin has dominion. It does mean we are weak vessels in a need of a savior. It does not mean we take advantage of God's great mercy either. It does mean that God loves us unconditionally. He is not mad at us or hates us. Yes, His wrath ( indescribable by human thought) will one day fall upon humanity but even that is brought about through His love. Because of my love for Him, I will not take advantage of that Grace. I will press forward with Him.
All the things I have done through the Lord and will do for Him in the future; I can only do through His grace. I am nothing without His grace. Grace is like the power of the Sun to Superman. Before I came to Christ, I was like Superman living on a planet with a red Sun. I was powerless and without hope. Now through Grace( the Yellow sun so to speak) I have the power to overcome. His Grace is more than sufficient enough for me. It is all I ever need and will need. It is all you will ever need and hope for as well.