Not that I have already obtained this or am already perfect, but I press on to make it my own, because Christ Jesus has made me his own. (ESV)
We know that as a believer in Jesus Christ there are parts of our lives that are pleasing to him and parts of our lives that need some work. The Apostle Paul was no different. Even though he had been used by God to start churches all over the known world, had performed miracles in Jesus' name, and had been used to bring thousands of people to faith, he was far from perfect.
In this effort to obtain perfection Paul knew that he was a work in progress. God is not content to leave us in the state he found us. He gives us a new heart, a new spirit, a new focus. We pursue Christ with all that we have. As the Holy Spirit enables and empowers us we are able to become more and more like him and we gain victory in those areas where we are less than perfect.
This progression in our spiritual lives whereby we are becoming more and more like Christ is what theologians call "sanctification," a setting apart of ourselves unto Christ, for his glory. Paul recognizes that he is in the process of sanctification. He is pressing on in this effort because of the work started in him by Christ.
If you belong to Jesus you have already been set apart by God. You have not been saved so that you can occupy space until the Lord returns. He wants to work in you and through you to bring the Gospel to others. You will be more effective in that work as you become more like Christ. Becoming more like Christ is the process of sanctification.
Paul was not perfect. Neither are we. But we are set apart by God to become more like Christ. Daily yield yourself to the work of the Holy Spirit. He will help you to become more like the Savior.