Paul had a one-track mind. His soul's single relentless passion is to press onward towards the goal to win the prize for which God had called him Heavenward in Christ Jesus, with all his might & effort without looking back. You cannot run forward effectively if you keep looking back. What is true physically is also true spiritually! Paul would not let the past (past guilt of persecuting Christians or past glory of his Jewish heritage & all his accomplishments) deter him from striving for what lied ahead and pressing on toward his goal to win the prize. He wanted to focus his energy and concentration on what God calls him to do, fixing his eyes on the finish line. Do not let your past (failures, sins, disappointments, discouragement) define you or distract you from being and doing what God calls you to be and do. Learn from your past mistakes and move on after you confess and repent. They're all forgiven. “I, even I, am He who blots out your transgressions, for my own sake, Forget (refusing to focus on) all the things you should have done but failed to do and all the things you did which you shouldn't have done. We also must refuse to allow past successes to inflate our pride or to make us think we've arrived spiritually. To dwell on these things can hinder our progress.
"More like the Master I would live and grow,
More of His love to others I would show;
More self-denial like His in Galilee,
More like the Master I long to ever be." (Gabriel)