In verses 10-14, he turns to the future. He looks forward toward his goal. Paul is not where he wants to be, not yet. Moreover, he is not planning to sit around idly waiting for a reward. Rather, Paul is determined to work, to press on.
The past will not hold him back. Paul is looking toward the future--straining forward to what lies ahead. I'm reminded of this week's reading from Isaiah "Do not remember the former things....I am about to do a new thing."
I am grateful to Carl R. Holladay for writing in Preaching Through the Christian Year C:
As we read these words closely, we see the nature of Paul's exchange: it was an exchange of something he actually possessed for something he might finally possess, the past for the future, past certainty for future hope. And this is what is especially instructive. As we experience loss, it is usually loss of the known, of what we own and have, whether it is our past or our possessions. As we lay all this aside for the superlative worth of Christ, we engage in a cardinal act of faith, for what we gain is a vision that is not ever fully ours until Christ makes us fully his won in the resurrection.