After repeating the unworthiness of his own efforts and achievements, Paul turns to the positive, and gives one the most encouraging passages in the entire letter to the church in Philippi.
You can see these encouraging words in Philippians 3:13-14:
Paul stresses an important point again for the third time: that of his own unworthiness and incompleteness. Of all people, Paul has the human credentials that would place him at the top. And yet, he sees those as inconsequential. In Christ, he is still straining forward, and his own efforts are not enough.
But Paul knows one thing for certain. This could be his life credo or motto. Paul leaves everything that he has accomplished behind. It holds no value compared to what he is striving for. This is the goal of his life, and should be the goal of ours as well.
Paul uses the imagery of a race here. For a runner, there is no looking back. A runner may occasionally glance to the side to see where his competition is, but this must not distract him from running the race. His eyes must remain on the goal. His efforts must be in striving for that goal.
Paul has forgotten what is behind. Certainly, this refers to his own achievements and accomplishments. But might it also include the wrongs done to him, the persecution received, the hurts received? Though this may not be the intent of his thoughts here, it definitely fits. We need to forget what lies behind, simply because it is behind us. Let us instead focus on what is ahead.